Merge ../linus

[mirror_ubuntu-zesty-kernel.git] / arch / um / drivers / ubd_kern.c

/*
 * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
 * Licensed under the GPL
 */

/* 2001-09-28...2002-04-17
 * Partition stuff by James_McMechan@hotmail.com
 * old style ubd by setting UBD_SHIFT to 0
 * 2002-09-27...2002-10-18 massive tinkering for 2.5
 * partitions have changed in 2.5
 * 2003-01-29 more tinkering for 2.5.59-1
 * This should now address the sysfs problems and has
 * the symlink for devfs to allow for booting with
 * the common /dev/ubd/discX/... names rather than
 * only /dev/ubdN/discN this version also has lots of
 * clean ups preparing for ubd-many.
 * James McMechan
 */

#define MAJOR_NR UBD_MAJOR
#define UBD_SHIFT 4

#include "linux/config.h"
#include "linux/module.h"
#include "linux/blkdev.h"
#include "linux/hdreg.h"
#include "linux/init.h"
#include "linux/devfs_fs_kernel.h"
#include "linux/cdrom.h"
#include "linux/proc_fs.h"
#include "linux/ctype.h"
#include "linux/capability.h"
#include "linux/mm.h"
#include "linux/vmalloc.h"
#include "linux/blkpg.h"
#include "linux/genhd.h"
#include "linux/spinlock.h"
#include "linux/platform_device.h"
#include "asm/segment.h"
#include "asm/uaccess.h"
#include "asm/irq.h"
#include "asm/types.h"
#include "asm/tlbflush.h"
#include "user_util.h"
#include "mem_user.h"
#include "kern_util.h"
#include "kern.h"
#include "mconsole_kern.h"
#include "init.h"
#include "irq_user.h"
#include "irq_kern.h"
#include "ubd_user.h"
#include "os.h"
#include "mem.h"
#include "mem_kern.h"
#include "cow.h"

enum ubd_req { UBD_READ, UBD_WRITE };

struct io_thread_req {
        enum ubd_req op;
        int fds[2];
        unsigned long offsets[2];
        unsigned long long offset;
        unsigned long length;
        char *buffer;
        int sectorsize;
        unsigned long sector_mask;
        unsigned long long cow_offset;
        unsigned long bitmap_words[2];
        int error;
};

extern int open_ubd_file(char *file, struct openflags *openflags, int shared,
                         char **backing_file_out, int *bitmap_offset_out,
                         unsigned long *bitmap_len_out, int *data_offset_out,
                         int *create_cow_out);
extern int create_cow_file(char *cow_file, char *backing_file,
                           struct openflags flags, int sectorsize,
                           int alignment, int *bitmap_offset_out,
                           unsigned long *bitmap_len_out,
                           int *data_offset_out);
extern int read_cow_bitmap(int fd, void *buf, int offset, int len);
extern void do_io(struct io_thread_req *req);

static inline int ubd_test_bit(__u64 bit, unsigned char *data)
{
        __u64 n;
        int bits, off;

        bits = sizeof(data[0]) * 8;
        n = bit / bits;
        off = bit % bits;
        return((data[n] & (1 << off)) != 0);
}

static inline void ubd_set_bit(__u64 bit, unsigned char *data)
{
        __u64 n;
        int bits, off;

        bits = sizeof(data[0]) * 8;
        n = bit / bits;
        off = bit % bits;
        data[n] |= (1 << off);
}
/*End stuff from ubd_user.h*/

#define DRIVER_NAME "uml-blkdev"

static DEFINE_SPINLOCK(ubd_io_lock);
static DEFINE_SPINLOCK(ubd_lock);

static void (*do_ubd)(void);

static int ubd_open(struct inode * inode, struct file * filp);
static int ubd_release(struct inode * inode, struct file * file);
static int ubd_ioctl(struct inode * inode, struct file * file,
                     unsigned int cmd, unsigned long arg);
static int ubd_getgeo(struct block_device *bdev, struct hd_geometry *geo);

#define MAX_DEV (8)

static struct block_device_operations ubd_blops = {
        .owner          = THIS_MODULE,
        .open           = ubd_open,
        .release        = ubd_release,
        .ioctl          = ubd_ioctl,
        .getgeo         = ubd_getgeo,
};

/* Protected by the queue_lock */
static request_queue_t *ubd_queue;

/* Protected by ubd_lock */
static int fake_major = MAJOR_NR;

static struct gendisk *ubd_gendisk[MAX_DEV];
static struct gendisk *fake_gendisk[MAX_DEV];

#ifdef CONFIG_BLK_DEV_UBD_SYNC
#define OPEN_FLAGS ((struct openflags) { .r = 1, .w = 1, .s = 1, .c = 0, \
                                         .cl = 1 })
#else
#define OPEN_FLAGS ((struct openflags) { .r = 1, .w = 1, .s = 0, .c = 0, \
                                         .cl = 1 })
#endif

/* Not protected - changed only in ubd_setup_common and then only to
 * to enable O_SYNC.
 */
static struct openflags global_openflags = OPEN_FLAGS;

struct cow {
        /* This is the backing file, actually */
        char *file;
        int fd;
        unsigned long *bitmap;
        unsigned long bitmap_len;
        int bitmap_offset;
        int data_offset;
};

struct ubd {
        char *file;
        int count;
        int fd;
        __u64 size;
        struct openflags boot_openflags;
        struct openflags openflags;
        int shared;
        int no_cow;
        struct cow cow;
        struct platform_device pdev;
};

#define DEFAULT_COW { \
        .file =                 NULL, \
        .fd =                   -1, \
        .bitmap =               NULL, \
        .bitmap_offset =        0, \
        .data_offset =          0, \
}

#define DEFAULT_UBD { \
        .file =                 NULL, \
        .count =                0, \
        .fd =                   -1, \
        .size =                 -1, \
        .boot_openflags =       OPEN_FLAGS, \
        .openflags =            OPEN_FLAGS, \
        .no_cow =               0, \
        .shared =               0, \
        .cow =                  DEFAULT_COW, \
}

struct ubd ubd_dev[MAX_DEV] = { [ 0 ... MAX_DEV - 1 ] = DEFAULT_UBD };

static int ubd0_init(void)
{
        struct ubd *dev = &ubd_dev[0];

        if(dev->file == NULL)
                dev->file = "root_fs";
        return(0);
}

__initcall(ubd0_init);

/* Only changed by fake_ide_setup which is a setup */
static int fake_ide = 0;
static struct proc_dir_entry *proc_ide_root = NULL;
static struct proc_dir_entry *proc_ide = NULL;

static void make_proc_ide(void)
{
        proc_ide_root = proc_mkdir("ide", NULL);
        proc_ide = proc_mkdir("ide0", proc_ide_root);
}

static int proc_ide_read_media(char *page, char **start, off_t off, int count,
                               int *eof, void *data)
{
        int len;

        strcpy(page, "disk\n");
        len = strlen("disk\n");
        len -= off;
        if (len < count){
                *eof = 1;
                if (len <= 0) return 0;
        }
        else len = count;
        *start = page + off;
        return len;
}

static void make_ide_entries(char *dev_name)
{
        struct proc_dir_entry *dir, *ent;
        char name[64];

        if(proc_ide_root == NULL) make_proc_ide();

        dir = proc_mkdir(dev_name, proc_ide);
        if(!dir) return;

        ent = create_proc_entry("media", S_IFREG|S_IRUGO, dir);
        if(!ent) return;
        ent->nlink = 1;
        ent->data = NULL;
        ent->read_proc = proc_ide_read_media;
        ent->write_proc = NULL;
        sprintf(name,"ide0/%s", dev_name);
        proc_symlink(dev_name, proc_ide_root, name);
}

static int fake_ide_setup(char *str)
{
        fake_ide = 1;
        return(1);
}

__setup("fake_ide", fake_ide_setup);

__uml_help(fake_ide_setup,
"fake_ide\n"
"    Create ide0 entries that map onto ubd devices.\n\n"
);

static int parse_unit(char **ptr)
{
        char *str = *ptr, *end;
        int n = -1;

        if(isdigit(*str)) {
                n = simple_strtoul(str, &end, 0);
                if(end == str)
                        return(-1);
                *ptr = end;
        }
        else if (('a' <= *str) && (*str <= 'h')) {
                n = *str - 'a';
                str++;
                *ptr = str;
        }
        return(n);
}

static int ubd_setup_common(char *str, int *index_out)
{
        struct ubd *dev;
        struct openflags flags = global_openflags;
        char *backing_file;
        int n, err, i;

        if(index_out) *index_out = -1;
        n = *str;
        if(n == '='){
                char *end;
                int major;

                str++;
                if(!strcmp(str, "sync")){
                        global_openflags = of_sync(global_openflags);
                        return(0);
                }
                major = simple_strtoul(str, &end, 0);
                if((*end != '\0') || (end == str)){
                        printk(KERN_ERR
                               "ubd_setup : didn't parse major number\n");
                        return(1);
                }

                err = 1;
                spin_lock(&ubd_lock);
                if(fake_major != MAJOR_NR){
                        printk(KERN_ERR "Can't assign a fake major twice\n");
                        goto out1;
                }

                fake_major = major;

                printk(KERN_INFO "Setting extra ubd major number to %d\n",
                       major);
                err = 0;
        out1:
                spin_unlock(&ubd_lock);
                return(err);
        }

        n = parse_unit(&str);
        if(n < 0){
                printk(KERN_ERR "ubd_setup : couldn't parse unit number "
                       "'%s'\n", str);
                return(1);
        }
        if(n >= MAX_DEV){
                printk(KERN_ERR "ubd_setup : index %d out of range "
                       "(%d devices, from 0 to %d)\n", n, MAX_DEV, MAX_DEV - 1);
                return(1);
        }

        err = 1;
        spin_lock(&ubd_lock);

        dev = &ubd_dev[n];
        if(dev->file != NULL){
                printk(KERN_ERR "ubd_setup : device already configured\n");
                goto out;
        }

        if (index_out)
                *index_out = n;

        for (i = 0; i < sizeof("rscd="); i++) {
                switch (*str) {
                case 'r':
                        flags.w = 0;
                        break;
                case 's':
                        flags.s = 1;
                        break;
                case 'd':
                        dev->no_cow = 1;
                        break;
                case 'c':
                        dev->shared = 1;
                        break;
                case '=':
                        str++;
                        goto break_loop;
                default:
                        printk(KERN_ERR "ubd_setup : Expected '=' or flag letter (r, s, c, or d)\n");
                        goto out;
                }
                str++;
        }

        if (*str == '=')
                printk(KERN_ERR "ubd_setup : Too many flags specified\n");
        else
                printk(KERN_ERR "ubd_setup : Expected '='\n");
        goto out;

break_loop:
        err = 0;
        backing_file = strchr(str, ',');

        if (!backing_file) {
                backing_file = strchr(str, ':');
        }

        if(backing_file){
                if(dev->no_cow)
                        printk(KERN_ERR "Can't specify both 'd' and a "
                               "cow file\n");
                else {
                        *backing_file = '\0';
                        backing_file++;
                }
        }
        dev->file = str;
        dev->cow.file = backing_file;
        dev->boot_openflags = flags;
out:
        spin_unlock(&ubd_lock);
        return(err);
}

static int ubd_setup(char *str)
{
        ubd_setup_common(str, NULL);
        return(1);
}

__setup("ubd", ubd_setup);
__uml_help(ubd_setup,
"ubd<n><flags>=<filename>[(:|,)<filename2>]\n"
"    This is used to associate a device with a file in the underlying\n"
"    filesystem. When specifying two filenames, the first one is the\n"
"    COW name and the second is the backing file name. As separator you can\n"
"    use either a ':' or a ',': the first one allows writing things like;\n"
"       ubd0=~/Uml/root_cow:~/Uml/root_backing_file\n"
"    while with a ',' the shell would not expand the 2nd '~'.\n"
"    When using only one filename, UML will detect whether to thread it like\n"
"    a COW file or a backing file. To override this detection, add the 'd'\n"
"    flag:\n"
"       ubd0d=BackingFile\n"
"    Usually, there is a filesystem in the file, but \n"
"    that's not required. Swap devices containing swap files can be\n"
"    specified like this. Also, a file which doesn't contain a\n"
"    filesystem can have its contents read in the virtual \n"
"    machine by running 'dd' on the device. <n> must be in the range\n"
"    0 to 7. Appending an 'r' to the number will cause that device\n"
"    to be mounted read-only. For example ubd1r=./ext_fs. Appending\n"
"    an 's' will cause data to be written to disk on the host immediately.\n\n"
);

static int udb_setup(char *str)
{
        printk("udb%s specified on command line is almost certainly a ubd -> "
               "udb TYPO\n", str);
        return(1);
}

__setup("udb", udb_setup);
__uml_help(udb_setup,
"udb\n"
"    This option is here solely to catch ubd -> udb typos, which can be\n"
"    to impossible to catch visually unless you specifically look for\n"
"    them.  The only result of any option starting with 'udb' is an error\n"
"    in the boot output.\n\n"
);

static int fakehd_set = 0;
static int fakehd(char *str)
{
        printk(KERN_INFO "fakehd : Changing ubd name to \"hd\".\n");
        fakehd_set = 1;
        return 1;
}

__setup("fakehd", fakehd);
__uml_help(fakehd,
"fakehd\n"
"    Change the ubd device name to \"hd\".\n\n"
);

static void do_ubd_request(request_queue_t * q);

/* Only changed by ubd_init, which is an initcall. */
int thread_fd = -1;

/* Changed by ubd_handler, which is serialized because interrupts only
 * happen on CPU 0.
 */
int intr_count = 0;

/* call ubd_finish if you need to serialize */
static void __ubd_finish(struct request *req, int error)
{
        int nsect;

        if(error){
                end_request(req, 0);
                return;
        }
        nsect = req->current_nr_sectors;
        req->sector += nsect;
        req->buffer += nsect << 9;
        req->errors = 0;
        req->nr_sectors -= nsect;
        req->current_nr_sectors = 0;
        end_request(req, 1);
}

static inline void ubd_finish(struct request *req, int error)
{
        spin_lock(&ubd_io_lock);
        __ubd_finish(req, error);
        spin_unlock(&ubd_io_lock);
}

/* Called without ubd_io_lock held */
static void ubd_handler(void)
{
        struct io_thread_req req;
        struct request *rq = elv_next_request(ubd_queue);
        int n;

        do_ubd = NULL;
        intr_count++;
        n = os_read_file(thread_fd, &req, sizeof(req));
        if(n != sizeof(req)){
                printk(KERN_ERR "Pid %d - spurious interrupt in ubd_handler, "
                       "err = %d\n", os_getpid(), -n);
                spin_lock(&ubd_io_lock);
                end_request(rq, 0);
                spin_unlock(&ubd_io_lock);
                return;
        }

        ubd_finish(rq, req.error);
        reactivate_fd(thread_fd, UBD_IRQ);      
        do_ubd_request(ubd_queue);
}

static irqreturn_t ubd_intr(int irq, void *dev, struct pt_regs *unused)
{
        ubd_handler();
        return(IRQ_HANDLED);
}

/* Only changed by ubd_init, which is an initcall. */
static int io_pid = -1;

void kill_io_thread(void)
{
        if(io_pid != -1)
                os_kill_process(io_pid, 1);
}

__uml_exitcall(kill_io_thread);

static int ubd_file_size(struct ubd *dev, __u64 *size_out)
{
        char *file;

        file = dev->cow.file ? dev->cow.file : dev->file;
        return(os_file_size(file, size_out));
}

static void ubd_close(struct ubd *dev)
{
        os_close_file(dev->fd);
        if(dev->cow.file == NULL)
                return;

        os_close_file(dev->cow.fd);
        vfree(dev->cow.bitmap);
        dev->cow.bitmap = NULL;
}

static int ubd_open_dev(struct ubd *dev)
{
        struct openflags flags;
        char **back_ptr;
        int err, create_cow, *create_ptr;

        dev->openflags = dev->boot_openflags;
        create_cow = 0;
        create_ptr = (dev->cow.file != NULL) ? &create_cow : NULL;
        back_ptr = dev->no_cow ? NULL : &dev->cow.file;
        dev->fd = open_ubd_file(dev->file, &dev->openflags, dev->shared,
                                back_ptr, &dev->cow.bitmap_offset,
                                &dev->cow.bitmap_len, &dev->cow.data_offset,
                                create_ptr);

        if((dev->fd == -ENOENT) && create_cow){
                dev->fd = create_cow_file(dev->file, dev->cow.file,
                                          dev->openflags, 1 << 9, PAGE_SIZE,
                                          &dev->cow.bitmap_offset,
                                          &dev->cow.bitmap_len,
                                          &dev->cow.data_offset);
                if(dev->fd >= 0){
                        printk(KERN_INFO "Creating \"%s\" as COW file for "
                               "\"%s\"\n", dev->file, dev->cow.file);
                }
        }

        if(dev->fd < 0){
                printk("Failed to open '%s', errno = %d\n", dev->file,
                       -dev->fd);
                return(dev->fd);
        }

        if(dev->cow.file != NULL){
                err = -ENOMEM;
                dev->cow.bitmap = (void *) vmalloc(dev->cow.bitmap_len);
                if(dev->cow.bitmap == NULL){
                        printk(KERN_ERR "Failed to vmalloc COW bitmap\n");
                        goto error;
                }
                flush_tlb_kernel_vm();

                err = read_cow_bitmap(dev->fd, dev->cow.bitmap,
                                      dev->cow.bitmap_offset,
                                      dev->cow.bitmap_len);
                if(err < 0)
                        goto error;

                flags = dev->openflags;
                flags.w = 0;
                err = open_ubd_file(dev->cow.file, &flags, dev->shared, NULL,
                                    NULL, NULL, NULL, NULL);
                if(err < 0) goto error;
                dev->cow.fd = err;
        }
        return(0);
 error:
        os_close_file(dev->fd);
        return(err);
}

static int ubd_new_disk(int major, u64 size, int unit,
                        struct gendisk **disk_out)
                        
{
        struct gendisk *disk;
        char from[sizeof("ubd/nnnnn\0")], to[sizeof("discnnnnn/disc\0")];
        int err;

        disk = alloc_disk(1 << UBD_SHIFT);
        if(disk == NULL)
                return(-ENOMEM);

        disk->major = major;
        disk->first_minor = unit << UBD_SHIFT;
        disk->fops = &ubd_blops;
        set_capacity(disk, size / 512);
        if(major == MAJOR_NR){
                sprintf(disk->disk_name, "ubd%c", 'a' + unit);
                sprintf(disk->devfs_name, "ubd/disc%d", unit);
                sprintf(from, "ubd/%d", unit);
                sprintf(to, "disc%d/disc", unit);
                err = devfs_mk_symlink(from, to);
                if(err)
                        printk("ubd_new_disk failed to make link from %s to "
                               "%s, error = %d\n", from, to, err);
        }
        else {
                sprintf(disk->disk_name, "ubd_fake%d", unit);
                sprintf(disk->devfs_name, "ubd_fake/disc%d", unit);
        }

        /* sysfs register (not for ide fake devices) */
        if (major == MAJOR_NR) {
                ubd_dev[unit].pdev.id   = unit;
                ubd_dev[unit].pdev.name = DRIVER_NAME;
                platform_device_register(&ubd_dev[unit].pdev);
                disk->driverfs_dev = &ubd_dev[unit].pdev.dev;
        }

        disk->private_data = &ubd_dev[unit];
        disk->queue = ubd_queue;
        add_disk(disk);

        *disk_out = disk;
        return 0;
}

#define ROUND_BLOCK(n) ((n + ((1 << 9) - 1)) & (-1 << 9))

static int ubd_add(int n)
{
        struct ubd *dev = &ubd_dev[n];
        int err;

        err = -ENODEV;
        if(dev->file == NULL)
                goto out;

        if (ubd_open_dev(dev))
                goto out;

        err = ubd_file_size(dev, &dev->size);
        if(err < 0)
                goto out_close;

        dev->size = ROUND_BLOCK(dev->size);

        err = ubd_new_disk(MAJOR_NR, dev->size, n, &ubd_gendisk[n]);
        if(err)
                goto out_close;

        if(fake_major != MAJOR_NR)
                ubd_new_disk(fake_major, dev->size, n,
                             &fake_gendisk[n]);

        /* perhaps this should also be under the "if (fake_major)" above */
        /* using the fake_disk->disk_name and also the fakehd_set name */
        if (fake_ide)
                make_ide_entries(ubd_gendisk[n]->disk_name);

        err = 0;
out_close:
        ubd_close(dev);
out:
        return err;
}

static int ubd_config(char *str)
{
        int n, err;

        str = kstrdup(str, GFP_KERNEL);
        if(str == NULL){
                printk(KERN_ERR "ubd_config failed to strdup string\n");
                return(1);
        }
        err = ubd_setup_common(str, &n);
        if(err){
                kfree(str);
                return(-1);
        }
        if(n == -1) return(0);

        spin_lock(&ubd_lock);
        err = ubd_add(n);
        if(err)
                ubd_dev[n].file = NULL;
        spin_unlock(&ubd_lock);

        return(err);
}

static int ubd_get_config(char *name, char *str, int size, char **error_out)
{
        struct ubd *dev;
        int n, len = 0;

        n = parse_unit(&name);
        if((n >= MAX_DEV) || (n < 0)){
                *error_out = "ubd_get_config : device number out of range";
                return(-1);
        }

        dev = &ubd_dev[n];
        spin_lock(&ubd_lock);

        if(dev->file == NULL){
                CONFIG_CHUNK(str, size, len, "", 1);
                goto out;
        }

        CONFIG_CHUNK(str, size, len, dev->file, 0);

        if(dev->cow.file != NULL){
                CONFIG_CHUNK(str, size, len, ",", 0);
                CONFIG_CHUNK(str, size, len, dev->cow.file, 1);
        }
        else CONFIG_CHUNK(str, size, len, "", 1);

 out:
        spin_unlock(&ubd_lock);
        return(len);
}

static int ubd_id(char **str, int *start_out, int *end_out)
{
        int n;

        n = parse_unit(str);
        *start_out = 0;
        *end_out = MAX_DEV - 1;
        return n;
}

static int ubd_remove(int n)
{
        struct ubd *dev;
        int err = -ENODEV;

        spin_lock(&ubd_lock);

        if(ubd_gendisk[n] == NULL)
                goto out;

        dev = &ubd_dev[n];

        if(dev->file == NULL)
                goto out;

        /* you cannot remove a open disk */
        err = -EBUSY;
        if(dev->count > 0)
                goto out;

        del_gendisk(ubd_gendisk[n]);
        put_disk(ubd_gendisk[n]);
        ubd_gendisk[n] = NULL;

        if(fake_gendisk[n] != NULL){
                del_gendisk(fake_gendisk[n]);
                put_disk(fake_gendisk[n]);
                fake_gendisk[n] = NULL;
        }

        platform_device_unregister(&dev->pdev);
        *dev = ((struct ubd) DEFAULT_UBD);
        err = 0;
out:
        spin_unlock(&ubd_lock);
        return err;
}

static struct mc_device ubd_mc = {
        .name           = "ubd",
        .config         = ubd_config,
        .get_config     = ubd_get_config,
        .id             = ubd_id,
        .remove         = ubd_remove,
};

static int ubd_mc_init(void)
{
        mconsole_register_dev(&ubd_mc);
        return 0;
}

__initcall(ubd_mc_init);

static struct platform_driver ubd_driver = {
        .driver = {
                .name  = DRIVER_NAME,
        },
};

int ubd_init(void)
{
        int i;

        devfs_mk_dir("ubd");
        if (register_blkdev(MAJOR_NR, "ubd"))
                return -1;

        ubd_queue = blk_init_queue(do_ubd_request, &ubd_io_lock);
        if (!ubd_queue) {
                unregister_blkdev(MAJOR_NR, "ubd");
                return -1;
        }
                
        if (fake_major != MAJOR_NR) {
                char name[sizeof("ubd_nnn\0")];

                snprintf(name, sizeof(name), "ubd_%d", fake_major);
                devfs_mk_dir(name);
                if (register_blkdev(fake_major, "ubd"))
                        return -1;
        }
        platform_driver_register(&ubd_driver);
        for (i = 0; i < MAX_DEV; i++)
                ubd_add(i);
        return 0;
}

late_initcall(ubd_init);

int ubd_driver_init(void){
        unsigned long stack;
        int err;

        /* Set by CONFIG_BLK_DEV_UBD_SYNC or ubd=sync.*/
        if(global_openflags.s){
                printk(KERN_INFO "ubd: Synchronous mode\n");
                /* Letting ubd=sync be like using ubd#s= instead of ubd#= is
                 * enough. So use anyway the io thread. */
        }
        stack = alloc_stack(0, 0);
        io_pid = start_io_thread(stack + PAGE_SIZE - sizeof(void *),
                                 &thread_fd);
        if(io_pid < 0){
                printk(KERN_ERR
                       "ubd : Failed to start I/O thread (errno = %d) - "
                       "falling back to synchronous I/O\n", -io_pid);
                io_pid = -1;
                return(0);
        }
        err = um_request_irq(UBD_IRQ, thread_fd, IRQ_READ, ubd_intr,
                             SA_INTERRUPT, "ubd", ubd_dev);
        if(err != 0)
                printk(KERN_ERR "um_request_irq failed - errno = %d\n", -err);
        return 0;
}

device_initcall(ubd_driver_init);

static int ubd_open(struct inode *inode, struct file *filp)
{
        struct gendisk *disk = inode->i_bdev->bd_disk;
        struct ubd *dev = disk->private_data;
        int err = 0;

        if(dev->count == 0){
                err = ubd_open_dev(dev);
                if(err){
                        printk(KERN_ERR "%s: Can't open \"%s\": errno = %d\n",
                               disk->disk_name, dev->file, -err);
                        goto out;
                }
        }
        dev->count++;
        set_disk_ro(disk, !dev->openflags.w);

        /* This should no more be needed. And it didn't work anyway to exclude
         * read-write remounting of filesystems.*/
        /*if((filp->f_mode & FMODE_WRITE) && !dev->openflags.w){
                if(--dev->count == 0) ubd_close(dev);
                err = -EROFS;
        }*/
 out:
        return(err);
}

static int ubd_release(struct inode * inode, struct file * file)
{
        struct gendisk *disk = inode->i_bdev->bd_disk;
        struct ubd *dev = disk->private_data;

        if(--dev->count == 0)
                ubd_close(dev);
        return(0);
}

static void cowify_bitmap(__u64 io_offset, int length, unsigned long *cow_mask,
                          __u64 *cow_offset, unsigned long *bitmap,
                          __u64 bitmap_offset, unsigned long *bitmap_words,
                          __u64 bitmap_len)
{
        __u64 sector = io_offset >> 9;
        int i, update_bitmap = 0;

        for(i = 0; i < length >> 9; i++){
                if(cow_mask != NULL)
                        ubd_set_bit(i, (unsigned char *) cow_mask);
                if(ubd_test_bit(sector + i, (unsigned char *) bitmap))
                        continue;

                update_bitmap = 1;
                ubd_set_bit(sector + i, (unsigned char *) bitmap);
        }

        if(!update_bitmap)
                return;

        *cow_offset = sector / (sizeof(unsigned long) * 8);

        /* This takes care of the case where we're exactly at the end of the
         * device, and *cow_offset + 1 is off the end.  So, just back it up
         * by one word.  Thanks to Lynn Kerby for the fix and James McMechan
         * for the original diagnosis.
         */
        if(*cow_offset == ((bitmap_len + sizeof(unsigned long) - 1) /
                           sizeof(unsigned long) - 1))
                (*cow_offset)--;

        bitmap_words[0] = bitmap[*cow_offset];
        bitmap_words[1] = bitmap[*cow_offset + 1];

        *cow_offset *= sizeof(unsigned long);
        *cow_offset += bitmap_offset;
}

static void cowify_req(struct io_thread_req *req, unsigned long *bitmap,
                       __u64 bitmap_offset, __u64 bitmap_len)
{
        __u64 sector = req->offset >> 9;
        int i;

        if(req->length > (sizeof(req->sector_mask) * 8) << 9)
                panic("Operation too long");

        if(req->op == UBD_READ) {
                for(i = 0; i < req->length >> 9; i++){
                        if(ubd_test_bit(sector + i, (unsigned char *) bitmap))
                                ubd_set_bit(i, (unsigned char *)
                                            &req->sector_mask);
                }
        }
        else cowify_bitmap(req->offset, req->length, &req->sector_mask,
                           &req->cow_offset, bitmap, bitmap_offset,
                           req->bitmap_words, bitmap_len);
}

/* Called with ubd_io_lock held */
static int prepare_request(struct request *req, struct io_thread_req *io_req)
{
        struct gendisk *disk = req->rq_disk;
        struct ubd *dev = disk->private_data;
        __u64 offset;
        int len;

        if(req->rq_status == RQ_INACTIVE) return(1);

        /* This should be impossible now */
        if((rq_data_dir(req) == WRITE) && !dev->openflags.w){
                printk("Write attempted on readonly ubd device %s\n",
                       disk->disk_name);
                end_request(req, 0);
                return(1);
        }

        offset = ((__u64) req->sector) << 9;
        len = req->current_nr_sectors << 9;

        io_req->fds[0] = (dev->cow.file != NULL) ? dev->cow.fd : dev->fd;
        io_req->fds[1] = dev->fd;
        io_req->cow_offset = -1;
        io_req->offset = offset;
        io_req->length = len;
        io_req->error = 0;
        io_req->sector_mask = 0;

        io_req->op = (rq_data_dir(req) == READ) ? UBD_READ : UBD_WRITE;
        io_req->offsets[0] = 0;
        io_req->offsets[1] = dev->cow.data_offset;
        io_req->buffer = req->buffer;
        io_req->sectorsize = 1 << 9;

        if(dev->cow.file != NULL)
                cowify_req(io_req, dev->cow.bitmap, dev->cow.bitmap_offset,
                           dev->cow.bitmap_len);

        return(0);
}

/* Called with ubd_io_lock held */
static void do_ubd_request(request_queue_t *q)
{
        struct io_thread_req io_req;
        struct request *req;
        int err, n;

        if(thread_fd == -1){
                while((req = elv_next_request(q)) != NULL){
                        err = prepare_request(req, &io_req);
                        if(!err){
                                do_io(&io_req);
                                __ubd_finish(req, io_req.error);
                        }
                }
        }
        else {
                if(do_ubd || (req = elv_next_request(q)) == NULL)
                        return;
                err = prepare_request(req, &io_req);
                if(!err){
                        do_ubd = ubd_handler;
                        n = os_write_file(thread_fd, (char *) &io_req,
                                         sizeof(io_req));
                        if(n != sizeof(io_req))
                                printk("write to io thread failed, "
                                       "errno = %d\n", -n);
                }
        }
}

static int ubd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
{
        struct ubd *dev = bdev->bd_disk->private_data;

        geo->heads = 128;
        geo->sectors = 32;
        geo->cylinders = dev->size / (128 * 32 * 512);
        return 0;
}

static int ubd_ioctl(struct inode * inode, struct file * file,
                     unsigned int cmd, unsigned long arg)
{
        struct ubd *dev = inode->i_bdev->bd_disk->private_data;
        struct hd_driveid ubd_id = {
                .cyls           = 0,
                .heads          = 128,
                .sectors        = 32,
        };

        switch (cmd) {
                struct cdrom_volctrl volume;
        case HDIO_GET_IDENTITY:
                ubd_id.cyls = dev->size / (128 * 32 * 512);
                if(copy_to_user((char __user *) arg, (char *) &ubd_id,
                                 sizeof(ubd_id)))
                        return(-EFAULT);
                return(0);
                
        case CDROMVOLREAD:
                if(copy_from_user(&volume, (char __user *) arg, sizeof(volume)))
                        return(-EFAULT);
                volume.channel0 = 255;
                volume.channel1 = 255;
                volume.channel2 = 255;
                volume.channel3 = 255;
                if(copy_to_user((char __user *) arg, &volume, sizeof(volume)))
                        return(-EFAULT);
                return(0);
        }
        return(-EINVAL);
}

static int path_requires_switch(char *from_cmdline, char *from_cow, char *cow)
{
        struct uml_stat buf1, buf2;
        int err;

        if(from_cmdline == NULL)
                return 0;
        if(!strcmp(from_cmdline, from_cow))
                return 0;

        err = os_stat_file(from_cmdline, &buf1);
        if(err < 0){
                printk("Couldn't stat '%s', err = %d\n", from_cmdline, -err);
                return 0;
        }
        err = os_stat_file(from_cow, &buf2);
        if(err < 0){
                printk("Couldn't stat '%s', err = %d\n", from_cow, -err);
                return 1;
        }
        if((buf1.ust_dev == buf2.ust_dev) && (buf1.ust_ino == buf2.ust_ino))
                return 0;

        printk("Backing file mismatch - \"%s\" requested,\n"
               "\"%s\" specified in COW header of \"%s\"\n",
               from_cmdline, from_cow, cow);
        return 1;
}

static int backing_file_mismatch(char *file, __u64 size, time_t mtime)
{
        unsigned long modtime;
        unsigned long long actual;
        int err;

        err = os_file_modtime(file, &modtime);
        if(err < 0){
                printk("Failed to get modification time of backing file "
                       "\"%s\", err = %d\n", file, -err);
                return(err);
        }

        err = os_file_size(file, &actual);
        if(err < 0){
                printk("Failed to get size of backing file \"%s\", "
                       "err = %d\n", file, -err);
                return(err);
        }

        if(actual != size){
                /*__u64 can be a long on AMD64 and with %lu GCC complains; so
                 * the typecast.*/
                printk("Size mismatch (%llu vs %llu) of COW header vs backing "
                       "file\n", (unsigned long long) size, actual);
                return(-EINVAL);
        }
        if(modtime != mtime){
                printk("mtime mismatch (%ld vs %ld) of COW header vs backing "
                       "file\n", mtime, modtime);
                return(-EINVAL);
        }
        return(0);
}

int read_cow_bitmap(int fd, void *buf, int offset, int len)
{
        int err;

        err = os_seek_file(fd, offset);
        if(err < 0)
                return(err);

        err = os_read_file(fd, buf, len);
        if(err < 0)
                return(err);

        return(0);
}

int open_ubd_file(char *file, struct openflags *openflags, int shared,
                  char **backing_file_out, int *bitmap_offset_out,
                  unsigned long *bitmap_len_out, int *data_offset_out,
                  int *create_cow_out)
{
        time_t mtime;
        unsigned long long size;
        __u32 version, align;
        char *backing_file;
        int fd, err, sectorsize, asked_switch, mode = 0644;

        fd = os_open_file(file, *openflags, mode);
        if (fd < 0) {
                if ((fd == -ENOENT) && (create_cow_out != NULL))
                        *create_cow_out = 1;
                if (!openflags->w ||
                   ((fd != -EROFS) && (fd != -EACCES)))
                        return fd;
                openflags->w = 0;
                fd = os_open_file(file, *openflags, mode);
                if (fd < 0)
                        return fd;
        }

        if(shared)
                printk("Not locking \"%s\" on the host\n", file);
        else {
                err = os_lock_file(fd, openflags->w);
                if(err < 0){
                        printk("Failed to lock '%s', err = %d\n", file, -err);
                        goto out_close;
                }
        }

        /* Succesful return case! */
        if(backing_file_out == NULL)
                return(fd);

        err = read_cow_header(file_reader, &fd, &version, &backing_file, &mtime,
                              &size, &sectorsize, &align, bitmap_offset_out);
        if(err && (*backing_file_out != NULL)){
                printk("Failed to read COW header from COW file \"%s\", "
                       "errno = %d\n", file, -err);
                goto out_close;
        }
        if(err)
                return(fd);

        asked_switch = path_requires_switch(*backing_file_out, backing_file, file);

        /* Allow switching only if no mismatch. */
        if (asked_switch && !backing_file_mismatch(*backing_file_out, size, mtime)) {
                printk("Switching backing file to '%s'\n", *backing_file_out);
                err = write_cow_header(file, fd, *backing_file_out,
                                       sectorsize, align, &size);
                if (err) {
                        printk("Switch failed, errno = %d\n", -err);
                        goto out_close;
                }
        } else {
                *backing_file_out = backing_file;
                err = backing_file_mismatch(*backing_file_out, size, mtime);
                if (err)
                        goto out_close;
        }

        cow_sizes(version, size, sectorsize, align, *bitmap_offset_out,
                  bitmap_len_out, data_offset_out);

        return fd;
 out_close:
        os_close_file(fd);
        return err;
}

int create_cow_file(char *cow_file, char *backing_file, struct openflags flags,
                    int sectorsize, int alignment, int *bitmap_offset_out,
                    unsigned long *bitmap_len_out, int *data_offset_out)
{
        int err, fd;

        flags.c = 1;
        fd = open_ubd_file(cow_file, &flags, 0, NULL, NULL, NULL, NULL, NULL);
        if(fd < 0){
                err = fd;
                printk("Open of COW file '%s' failed, errno = %d\n", cow_file,
                       -err);
                goto out;
        }

        err = init_cow_file(fd, cow_file, backing_file, sectorsize, alignment,
                            bitmap_offset_out, bitmap_len_out,
                            data_offset_out);
        if(!err)
                return(fd);
        os_close_file(fd);
 out:
        return(err);
}

static int update_bitmap(struct io_thread_req *req)
{
        int n;

        if(req->cow_offset == -1)
                return(0);

        n = os_seek_file(req->fds[1], req->cow_offset);
        if(n < 0){
                printk("do_io - bitmap lseek failed : err = %d\n", -n);
                return(1);
        }

        n = os_write_file(req->fds[1], &req->bitmap_words,
                          sizeof(req->bitmap_words));
        if(n != sizeof(req->bitmap_words)){
                printk("do_io - bitmap update failed, err = %d fd = %d\n", -n,
                       req->fds[1]);
                return(1);
        }

        return(0);
}

void do_io(struct io_thread_req *req)
{
        char *buf;
        unsigned long len;
        int n, nsectors, start, end, bit;
        int err;
        __u64 off;

        nsectors = req->length / req->sectorsize;
        start = 0;
        do {
                bit = ubd_test_bit(start, (unsigned char *) &req->sector_mask);
                end = start;
                while((end < nsectors) &&
                      (ubd_test_bit(end, (unsigned char *)
                                    &req->sector_mask) == bit))
                        end++;

                off = req->offset + req->offsets[bit] +
                        start * req->sectorsize;
                len = (end - start) * req->sectorsize;
                buf = &req->buffer[start * req->sectorsize];

                err = os_seek_file(req->fds[bit], off);
                if(err < 0){
                        printk("do_io - lseek failed : err = %d\n", -err);
                        req->error = 1;
                        return;
                }
                if(req->op == UBD_READ){
                        n = 0;
                        do {
                                buf = &buf[n];
                                len -= n;
                                n = os_read_file(req->fds[bit], buf, len);
                                if (n < 0) {
                                        printk("do_io - read failed, err = %d "
                                               "fd = %d\n", -n, req->fds[bit]);
                                        req->error = 1;
                                        return;
                                }
                        } while((n < len) && (n != 0));
                        if (n < len) memset(&buf[n], 0, len - n);
                } else {
                        n = os_write_file(req->fds[bit], buf, len);
                        if(n != len){
                                printk("do_io - write failed err = %d "
                                       "fd = %d\n", -n, req->fds[bit]);
                                req->error = 1;
                                return;
                        }
                }

                start = end;
        } while(start < nsectors);

        req->error = update_bitmap(req);
}

/* Changed in start_io_thread, which is serialized by being called only
 * from ubd_init, which is an initcall.
 */
int kernel_fd = -1;

/* Only changed by the io thread */
int io_count = 0;

int io_thread(void *arg)
{
        struct io_thread_req req;
        int n;

        ignore_sigwinch_sig();
        while(1){
                n = os_read_file(kernel_fd, &req, sizeof(req));
                if(n != sizeof(req)){
                        if(n < 0)
                                printk("io_thread - read failed, fd = %d, "
                                       "err = %d\n", kernel_fd, -n);
                        else {
                                printk("io_thread - short read, fd = %d, "
                                       "length = %d\n", kernel_fd, n);
                        }
                        continue;
                }
                io_count++;
                do_io(&req);
                n = os_write_file(kernel_fd, &req, sizeof(req));
                if(n != sizeof(req))
                        printk("io_thread - write failed, fd = %d, err = %d\n",
                               kernel_fd, -n);
        }

        return 0;
}