pnfs: layoutget rpc code cleanup

[mirror_ubuntu-artful-kernel.git] / fs / nfs / pnfs.c

/*
 *  pNFS functions to call and manage layout drivers.
 *
 *  Copyright (c) 2002 [year of first publication]
 *  The Regents of the University of Michigan
 *  All Rights Reserved
 *
 *  Dean Hildebrand <dhildebz@umich.edu>
 *
 *  Permission is granted to use, copy, create derivative works, and
 *  redistribute this software and such derivative works for any purpose,
 *  so long as the name of the University of Michigan is not used in
 *  any advertising or publicity pertaining to the use or distribution
 *  of this software without specific, written prior authorization. If
 *  the above copyright notice or any other identification of the
 *  University of Michigan is included in any copy of any portion of
 *  this software, then the disclaimer below must also be included.
 *
 *  This software is provided as is, without representation or warranty
 *  of any kind either express or implied, including without limitation
 *  the implied warranties of merchantability, fitness for a particular
 *  purpose, or noninfringement.  The Regents of the University of
 *  Michigan shall not be liable for any damages, including special,
 *  indirect, incidental, or consequential damages, with respect to any
 *  claim arising out of or in connection with the use of the software,
 *  even if it has been or is hereafter advised of the possibility of
 *  such damages.
 */

#include <linux/nfs_fs.h>
#include "internal.h"
#include "pnfs.h"

#define NFSDBG_FACILITY         NFSDBG_PNFS

/* Locking:
 *
 * pnfs_spinlock:
 *      protects pnfs_modules_tbl.
 */
static DEFINE_SPINLOCK(pnfs_spinlock);

/*
 * pnfs_modules_tbl holds all pnfs modules
 */
static LIST_HEAD(pnfs_modules_tbl);

/* Return the registered pnfs layout driver module matching given id */
static struct pnfs_layoutdriver_type *
find_pnfs_driver_locked(u32 id)
{
        struct pnfs_layoutdriver_type *local;

        list_for_each_entry(local, &pnfs_modules_tbl, pnfs_tblid)
                if (local->id == id)
                        goto out;
        local = NULL;
out:
        dprintk("%s: Searching for id %u, found %p\n", __func__, id, local);
        return local;
}

static struct pnfs_layoutdriver_type *
find_pnfs_driver(u32 id)
{
        struct pnfs_layoutdriver_type *local;

        spin_lock(&pnfs_spinlock);
        local = find_pnfs_driver_locked(id);
        spin_unlock(&pnfs_spinlock);
        return local;
}

void
unset_pnfs_layoutdriver(struct nfs_server *nfss)
{
        if (nfss->pnfs_curr_ld) {
                nfss->pnfs_curr_ld->clear_layoutdriver(nfss);
                module_put(nfss->pnfs_curr_ld->owner);
        }
        nfss->pnfs_curr_ld = NULL;
}

/*
 * Try to set the server's pnfs module to the pnfs layout type specified by id.
 * Currently only one pNFS layout driver per filesystem is supported.
 *
 * @id layout type. Zero (illegal layout type) indicates pNFS not in use.
 */
void
set_pnfs_layoutdriver(struct nfs_server *server, u32 id)
{
        struct pnfs_layoutdriver_type *ld_type = NULL;

        if (id == 0)
                goto out_no_driver;
        if (!(server->nfs_client->cl_exchange_flags &
                 (EXCHGID4_FLAG_USE_NON_PNFS | EXCHGID4_FLAG_USE_PNFS_MDS))) {
                printk(KERN_ERR "%s: id %u cl_exchange_flags 0x%x\n", __func__,
                       id, server->nfs_client->cl_exchange_flags);
                goto out_no_driver;
        }
        ld_type = find_pnfs_driver(id);
        if (!ld_type) {
                request_module("%s-%u", LAYOUT_NFSV4_1_MODULE_PREFIX, id);
                ld_type = find_pnfs_driver(id);
                if (!ld_type) {
                        dprintk("%s: No pNFS module found for %u.\n",
                                __func__, id);
                        goto out_no_driver;
                }
        }
        if (!try_module_get(ld_type->owner)) {
                dprintk("%s: Could not grab reference on module\n", __func__);
                goto out_no_driver;
        }
        server->pnfs_curr_ld = ld_type;
        if (ld_type->set_layoutdriver(server)) {
                printk(KERN_ERR
                       "%s: Error initializing mount point for layout driver %u.\n",
                       __func__, id);
                module_put(ld_type->owner);
                goto out_no_driver;
        }
        dprintk("%s: pNFS module for %u set\n", __func__, id);
        return;

out_no_driver:
        dprintk("%s: Using NFSv4 I/O\n", __func__);
        server->pnfs_curr_ld = NULL;
}

int
pnfs_register_layoutdriver(struct pnfs_layoutdriver_type *ld_type)
{
        int status = -EINVAL;
        struct pnfs_layoutdriver_type *tmp;

        if (ld_type->id == 0) {
                printk(KERN_ERR "%s id 0 is reserved\n", __func__);
                return status;
        }
        if (!ld_type->alloc_lseg || !ld_type->free_lseg) {
                printk(KERN_ERR "%s Layout driver must provide "
                       "alloc_lseg and free_lseg.\n", __func__);
                return status;
        }

        spin_lock(&pnfs_spinlock);
        tmp = find_pnfs_driver_locked(ld_type->id);
        if (!tmp) {
                list_add(&ld_type->pnfs_tblid, &pnfs_modules_tbl);
                status = 0;
                dprintk("%s Registering id:%u name:%s\n", __func__, ld_type->id,
                        ld_type->name);
        } else {
                printk(KERN_ERR "%s Module with id %d already loaded!\n",
                        __func__, ld_type->id);
        }
        spin_unlock(&pnfs_spinlock);

        return status;
}
EXPORT_SYMBOL_GPL(pnfs_register_layoutdriver);

void
pnfs_unregister_layoutdriver(struct pnfs_layoutdriver_type *ld_type)
{
        dprintk("%s Deregistering id:%u\n", __func__, ld_type->id);
        spin_lock(&pnfs_spinlock);
        list_del(&ld_type->pnfs_tblid);
        spin_unlock(&pnfs_spinlock);
}
EXPORT_SYMBOL_GPL(pnfs_unregister_layoutdriver);

/*
 * pNFS client layout cache
 */

static void
get_layout_hdr_locked(struct pnfs_layout_hdr *lo)
{
        assert_spin_locked(&lo->plh_inode->i_lock);
        lo->plh_refcount++;
}

static void
put_layout_hdr_locked(struct pnfs_layout_hdr *lo)
{
        assert_spin_locked(&lo->plh_inode->i_lock);
        BUG_ON(lo->plh_refcount == 0);

        lo->plh_refcount--;
        if (!lo->plh_refcount) {
                dprintk("%s: freeing layout cache %p\n", __func__, lo);
                BUG_ON(!list_empty(&lo->plh_layouts));
                NFS_I(lo->plh_inode)->layout = NULL;
                kfree(lo);
        }
}

void
put_layout_hdr(struct inode *inode)
{
        spin_lock(&inode->i_lock);
        put_layout_hdr_locked(NFS_I(inode)->layout);
        spin_unlock(&inode->i_lock);
}

static void
init_lseg(struct pnfs_layout_hdr *lo, struct pnfs_layout_segment *lseg)
{
        INIT_LIST_HEAD(&lseg->pls_list);
        atomic_set(&lseg->pls_refcount, 1);
        smp_mb();
        set_bit(NFS_LSEG_VALID, &lseg->pls_flags);
        lseg->pls_layout = lo;
}

static void free_lseg(struct pnfs_layout_segment *lseg)
{
        struct inode *ino = lseg->pls_layout->plh_inode;

        NFS_SERVER(ino)->pnfs_curr_ld->free_lseg(lseg);
        /* Matched by get_layout_hdr in pnfs_insert_layout */
        put_layout_hdr(ino);
}

/* The use of tmp_list is necessary because pnfs_curr_ld->free_lseg
 * could sleep, so must be called outside of the lock.
 * Returns 1 if object was removed, otherwise return 0.
 */
static int
put_lseg_locked(struct pnfs_layout_segment *lseg,
                struct list_head *tmp_list)
{
        dprintk("%s: lseg %p ref %d valid %d\n", __func__, lseg,
                atomic_read(&lseg->pls_refcount),
                test_bit(NFS_LSEG_VALID, &lseg->pls_flags));
        if (atomic_dec_and_test(&lseg->pls_refcount)) {
                struct inode *ino = lseg->pls_layout->plh_inode;

                BUG_ON(test_bit(NFS_LSEG_VALID, &lseg->pls_flags));
                list_del(&lseg->pls_list);
                if (list_empty(&lseg->pls_layout->plh_segs)) {
                        struct nfs_client *clp;

                        clp = NFS_SERVER(ino)->nfs_client;
                        spin_lock(&clp->cl_lock);
                        /* List does not take a reference, so no need for put here */
                        list_del_init(&lseg->pls_layout->plh_layouts);
                        spin_unlock(&clp->cl_lock);
                }
                list_add(&lseg->pls_list, tmp_list);
                return 1;
        }
        return 0;
}

static bool
should_free_lseg(u32 lseg_iomode, u32 recall_iomode)
{
        return (recall_iomode == IOMODE_ANY ||
                lseg_iomode == recall_iomode);
}

/* Returns 1 if lseg is removed from list, 0 otherwise */
static int mark_lseg_invalid(struct pnfs_layout_segment *lseg,
                             struct list_head *tmp_list)
{
        int rv = 0;

        if (test_and_clear_bit(NFS_LSEG_VALID, &lseg->pls_flags)) {
                /* Remove the reference keeping the lseg in the
                 * list.  It will now be removed when all
                 * outstanding io is finished.
                 */
                rv = put_lseg_locked(lseg, tmp_list);
        }
        return rv;
}

/* Returns count of number of matching invalid lsegs remaining in list
 * after call.
 */
static int
mark_matching_lsegs_invalid(struct pnfs_layout_hdr *lo,
                            struct list_head *tmp_list,
                            u32 iomode)
{
        struct pnfs_layout_segment *lseg, *next;
        int invalid = 0, removed = 0;

        dprintk("%s:Begin lo %p\n", __func__, lo);

        list_for_each_entry_safe(lseg, next, &lo->plh_segs, pls_list)
                if (should_free_lseg(lseg->pls_range.iomode, iomode)) {
                        dprintk("%s: freeing lseg %p iomode %d "
                                "offset %llu length %llu\n", __func__,
                                lseg, lseg->pls_range.iomode, lseg->pls_range.offset,
                                lseg->pls_range.length);
                        invalid++;
                        removed += mark_lseg_invalid(lseg, tmp_list);
                }
        dprintk("%s:Return %i\n", __func__, invalid - removed);
        return invalid - removed;
}

static void
pnfs_free_lseg_list(struct list_head *free_me)
{
        struct pnfs_layout_segment *lseg, *tmp;

        list_for_each_entry_safe(lseg, tmp, free_me, pls_list) {
                list_del(&lseg->pls_list);
                free_lseg(lseg);
        }
}

void
pnfs_destroy_layout(struct nfs_inode *nfsi)
{
        struct pnfs_layout_hdr *lo;
        LIST_HEAD(tmp_list);

        spin_lock(&nfsi->vfs_inode.i_lock);
        lo = nfsi->layout;
        if (lo) {
                set_bit(NFS_LAYOUT_DESTROYED, &nfsi->layout->plh_flags);
                mark_matching_lsegs_invalid(lo, &tmp_list, IOMODE_ANY);
                /* Matched by refcount set to 1 in alloc_init_layout_hdr */
                put_layout_hdr_locked(lo);
        }
        spin_unlock(&nfsi->vfs_inode.i_lock);
        pnfs_free_lseg_list(&tmp_list);
}

/*
 * Called by the state manger to remove all layouts established under an
 * expired lease.
 */
void
pnfs_destroy_all_layouts(struct nfs_client *clp)
{
        struct pnfs_layout_hdr *lo;
        LIST_HEAD(tmp_list);

        spin_lock(&clp->cl_lock);
        list_splice_init(&clp->cl_layouts, &tmp_list);
        spin_unlock(&clp->cl_lock);

        while (!list_empty(&tmp_list)) {
                lo = list_entry(tmp_list.next, struct pnfs_layout_hdr,
                                plh_layouts);
                dprintk("%s freeing layout for inode %lu\n", __func__,
                        lo->plh_inode->i_ino);
                pnfs_destroy_layout(NFS_I(lo->plh_inode));
        }
}

/* update lo->plh_stateid with new if is more recent */
static void
pnfs_set_layout_stateid(struct pnfs_layout_hdr *lo,
                        const nfs4_stateid *new)
{
        u32 oldseq, newseq;

        oldseq = be32_to_cpu(lo->plh_stateid.stateid.seqid);
        newseq = be32_to_cpu(new->stateid.seqid);
        if ((int)(newseq - oldseq) > 0)
                memcpy(&lo->plh_stateid, &new->stateid, sizeof(new->stateid));
}

int
pnfs_choose_layoutget_stateid(nfs4_stateid *dst, struct pnfs_layout_hdr *lo,
                              struct nfs4_state *open_state)
{
        int status = 0;

        dprintk("--> %s\n", __func__);
        spin_lock(&lo->plh_inode->i_lock);
        if (list_empty(&lo->plh_segs)) {
                int seq;

                do {
                        seq = read_seqbegin(&open_state->seqlock);
                        memcpy(dst->data, open_state->stateid.data,
                               sizeof(open_state->stateid.data));
                } while (read_seqretry(&open_state->seqlock, seq));
        } else
                memcpy(dst->data, lo->plh_stateid.data, sizeof(lo->plh_stateid.data));
        spin_unlock(&lo->plh_inode->i_lock);
        dprintk("<-- %s\n", __func__);
        return status;
}

/*
* Get layout from server.
*    for now, assume that whole file layouts are requested.
*    arg->offset: 0
*    arg->length: all ones
*/
static struct pnfs_layout_segment *
send_layoutget(struct pnfs_layout_hdr *lo,
           struct nfs_open_context *ctx,
           u32 iomode)
{
        struct inode *ino = lo->plh_inode;
        struct nfs_server *server = NFS_SERVER(ino);
        struct nfs4_layoutget *lgp;
        struct pnfs_layout_segment *lseg = NULL;

        dprintk("--> %s\n", __func__);

        BUG_ON(ctx == NULL);
        lgp = kzalloc(sizeof(*lgp), GFP_KERNEL);
        if (lgp == NULL) {
                put_layout_hdr(lo->plh_inode);
                return NULL;
        }
        lgp->args.minlength = NFS4_MAX_UINT64;
        lgp->args.maxcount = PNFS_LAYOUT_MAXSIZE;
        lgp->args.range.iomode = iomode;
        lgp->args.range.offset = 0;
        lgp->args.range.length = NFS4_MAX_UINT64;
        lgp->args.type = server->pnfs_curr_ld->id;
        lgp->args.inode = ino;
        lgp->args.ctx = get_nfs_open_context(ctx);
        lgp->lsegpp = &lseg;

        /* Synchronously retrieve layout information from server and
         * store in lseg.
         */
        nfs4_proc_layoutget(lgp);
        if (!lseg) {
                /* remember that LAYOUTGET failed and suspend trying */
                set_bit(lo_fail_bit(iomode), &lo->plh_flags);
        }
        return lseg;
}

/*
 * Compare two layout segments for sorting into layout cache.
 * We want to preferentially return RW over RO layouts, so ensure those
 * are seen first.
 */
static s64
cmp_layout(u32 iomode1, u32 iomode2)
{
        /* read > read/write */
        return (int)(iomode2 == IOMODE_READ) - (int)(iomode1 == IOMODE_READ);
}

static void
pnfs_insert_layout(struct pnfs_layout_hdr *lo,
                   struct pnfs_layout_segment *lseg)
{
        struct pnfs_layout_segment *lp;
        int found = 0;

        dprintk("%s:Begin\n", __func__);

        assert_spin_locked(&lo->plh_inode->i_lock);
        if (list_empty(&lo->plh_segs)) {
                struct nfs_client *clp = NFS_SERVER(lo->plh_inode)->nfs_client;

                spin_lock(&clp->cl_lock);
                BUG_ON(!list_empty(&lo->plh_layouts));
                list_add_tail(&lo->plh_layouts, &clp->cl_layouts);
                spin_unlock(&clp->cl_lock);
        }
        list_for_each_entry(lp, &lo->plh_segs, pls_list) {
                if (cmp_layout(lp->pls_range.iomode, lseg->pls_range.iomode) > 0)
                        continue;
                list_add_tail(&lseg->pls_list, &lp->pls_list);
                dprintk("%s: inserted lseg %p "
                        "iomode %d offset %llu length %llu before "
                        "lp %p iomode %d offset %llu length %llu\n",
                        __func__, lseg, lseg->pls_range.iomode,
                        lseg->pls_range.offset, lseg->pls_range.length,
                        lp, lp->pls_range.iomode, lp->pls_range.offset,
                        lp->pls_range.length);
                found = 1;
                break;
        }
        if (!found) {
                list_add_tail(&lseg->pls_list, &lo->plh_segs);
                dprintk("%s: inserted lseg %p "
                        "iomode %d offset %llu length %llu at tail\n",
                        __func__, lseg, lseg->pls_range.iomode,
                        lseg->pls_range.offset, lseg->pls_range.length);
        }
        get_layout_hdr_locked(lo);

        dprintk("%s:Return\n", __func__);
}

static struct pnfs_layout_hdr *
alloc_init_layout_hdr(struct inode *ino)
{
        struct pnfs_layout_hdr *lo;

        lo = kzalloc(sizeof(struct pnfs_layout_hdr), GFP_KERNEL);
        if (!lo)
                return NULL;
        lo->plh_refcount = 1;
        INIT_LIST_HEAD(&lo->plh_layouts);
        INIT_LIST_HEAD(&lo->plh_segs);
        lo->plh_inode = ino;
        return lo;
}

static struct pnfs_layout_hdr *
pnfs_find_alloc_layout(struct inode *ino)
{
        struct nfs_inode *nfsi = NFS_I(ino);
        struct pnfs_layout_hdr *new = NULL;

        dprintk("%s Begin ino=%p layout=%p\n", __func__, ino, nfsi->layout);

        assert_spin_locked(&ino->i_lock);
        if (nfsi->layout) {
                if (test_bit(NFS_LAYOUT_DESTROYED, &nfsi->layout->plh_flags))
                        return NULL;
                else
                        return nfsi->layout;
        }
        spin_unlock(&ino->i_lock);
        new = alloc_init_layout_hdr(ino);
        spin_lock(&ino->i_lock);

        if (likely(nfsi->layout == NULL))       /* Won the race? */
                nfsi->layout = new;
        else
                kfree(new);
        return nfsi->layout;
}

/*
 * iomode matching rules:
 * iomode       lseg    match
 * -----        -----   -----
 * ANY          READ    true
 * ANY          RW      true
 * RW           READ    false
 * RW           RW      true
 * READ         READ    true
 * READ         RW      true
 */
static int
is_matching_lseg(struct pnfs_layout_segment *lseg, u32 iomode)
{
        return (iomode != IOMODE_RW || lseg->pls_range.iomode == IOMODE_RW);
}

/*
 * lookup range in layout
 */
static struct pnfs_layout_segment *
pnfs_has_layout(struct pnfs_layout_hdr *lo, u32 iomode)
{
        struct pnfs_layout_segment *lseg, *ret = NULL;

        dprintk("%s:Begin\n", __func__);

        assert_spin_locked(&lo->plh_inode->i_lock);
        list_for_each_entry(lseg, &lo->plh_segs, pls_list) {
                if (test_bit(NFS_LSEG_VALID, &lseg->pls_flags) &&
                    is_matching_lseg(lseg, iomode)) {
                        ret = lseg;
                        break;
                }
                if (cmp_layout(iomode, lseg->pls_range.iomode) > 0)
                        break;
        }

        dprintk("%s:Return lseg %p ref %d\n",
                __func__, ret, ret ? atomic_read(&ret->pls_refcount) : 0);
        return ret;
}

/*
 * Layout segment is retreived from the server if not cached.
 * The appropriate layout segment is referenced and returned to the caller.
 */
struct pnfs_layout_segment *
pnfs_update_layout(struct inode *ino,
                   struct nfs_open_context *ctx,
                   enum pnfs_iomode iomode)
{
        struct nfs_inode *nfsi = NFS_I(ino);
        struct pnfs_layout_hdr *lo;
        struct pnfs_layout_segment *lseg = NULL;

        if (!pnfs_enabled_sb(NFS_SERVER(ino)))
                return NULL;
        spin_lock(&ino->i_lock);
        lo = pnfs_find_alloc_layout(ino);
        if (lo == NULL) {
                dprintk("%s ERROR: can't get pnfs_layout_hdr\n", __func__);
                goto out_unlock;
        }

        /* Check to see if the layout for the given range already exists */
        lseg = pnfs_has_layout(lo, iomode);
        if (lseg) {
                dprintk("%s: Using cached lseg %p for iomode %d)\n",
                        __func__, lseg, iomode);
                goto out_unlock;
        }

        /* if LAYOUTGET already failed once we don't try again */
        if (test_bit(lo_fail_bit(iomode), &nfsi->layout->plh_flags))
                goto out_unlock;

        get_layout_hdr_locked(lo); /* Matched in nfs4_layoutget_release */
        spin_unlock(&ino->i_lock);

        lseg = send_layoutget(lo, ctx, iomode);
out:
        dprintk("%s end, state 0x%lx lseg %p\n", __func__,
                nfsi->layout->plh_flags, lseg);
        return lseg;
out_unlock:
        spin_unlock(&ino->i_lock);
        goto out;
}

int
pnfs_layout_process(struct nfs4_layoutget *lgp)
{
        struct pnfs_layout_hdr *lo = NFS_I(lgp->args.inode)->layout;
        struct nfs4_layoutget_res *res = &lgp->res;
        struct pnfs_layout_segment *lseg;
        struct inode *ino = lo->plh_inode;
        int status = 0;

        /* Inject layout blob into I/O device driver */
        lseg = NFS_SERVER(ino)->pnfs_curr_ld->alloc_lseg(lo, res);
        if (!lseg || IS_ERR(lseg)) {
                if (!lseg)
                        status = -ENOMEM;
                else
                        status = PTR_ERR(lseg);
                dprintk("%s: Could not allocate layout: error %d\n",
                       __func__, status);
                goto out;
        }

        spin_lock(&ino->i_lock);
        init_lseg(lo, lseg);
        lseg->pls_range = res->range;
        *lgp->lsegpp = lseg;
        pnfs_insert_layout(lo, lseg);

        /* Done processing layoutget. Set the layout stateid */
        pnfs_set_layout_stateid(lo, &res->stateid);
        spin_unlock(&ino->i_lock);
out:
        return status;
}

/*
 * Device ID cache. Currently supports one layout type per struct nfs_client.
 * Add layout type to the lookup key to expand to support multiple types.
 */
int
pnfs_alloc_init_deviceid_cache(struct nfs_client *clp,
                         void (*free_callback)(struct pnfs_deviceid_node *))
{
        struct pnfs_deviceid_cache *c;

        c = kzalloc(sizeof(struct pnfs_deviceid_cache), GFP_KERNEL);
        if (!c)
                return -ENOMEM;
        spin_lock(&clp->cl_lock);
        if (clp->cl_devid_cache != NULL) {
                atomic_inc(&clp->cl_devid_cache->dc_ref);
                dprintk("%s [kref [%d]]\n", __func__,
                        atomic_read(&clp->cl_devid_cache->dc_ref));
                kfree(c);
        } else {
                /* kzalloc initializes hlists */
                spin_lock_init(&c->dc_lock);
                atomic_set(&c->dc_ref, 1);
                c->dc_free_callback = free_callback;
                clp->cl_devid_cache = c;
                dprintk("%s [new]\n", __func__);
        }
        spin_unlock(&clp->cl_lock);
        return 0;
}
EXPORT_SYMBOL_GPL(pnfs_alloc_init_deviceid_cache);

/*
 * Called from pnfs_layoutdriver_type->free_lseg
 * last layout segment reference frees deviceid
 */
void
pnfs_put_deviceid(struct pnfs_deviceid_cache *c,
                  struct pnfs_deviceid_node *devid)
{
        struct nfs4_deviceid *id = &devid->de_id;
        struct pnfs_deviceid_node *d;
        struct hlist_node *n;
        long h = nfs4_deviceid_hash(id);

        dprintk("%s [%d]\n", __func__, atomic_read(&devid->de_ref));
        if (!atomic_dec_and_lock(&devid->de_ref, &c->dc_lock))
                return;

        hlist_for_each_entry_rcu(d, n, &c->dc_deviceids[h], de_node)
                if (!memcmp(&d->de_id, id, sizeof(*id))) {
                        hlist_del_rcu(&d->de_node);
                        spin_unlock(&c->dc_lock);
                        synchronize_rcu();
                        c->dc_free_callback(devid);
                        return;
                }
        spin_unlock(&c->dc_lock);
        /* Why wasn't it found in  the list? */
        BUG();
}
EXPORT_SYMBOL_GPL(pnfs_put_deviceid);

/* Find and reference a deviceid */
struct pnfs_deviceid_node *
pnfs_find_get_deviceid(struct pnfs_deviceid_cache *c, struct nfs4_deviceid *id)
{
        struct pnfs_deviceid_node *d;
        struct hlist_node *n;
        long hash = nfs4_deviceid_hash(id);

        dprintk("--> %s hash %ld\n", __func__, hash);
        rcu_read_lock();
        hlist_for_each_entry_rcu(d, n, &c->dc_deviceids[hash], de_node) {
                if (!memcmp(&d->de_id, id, sizeof(*id))) {
                        if (!atomic_inc_not_zero(&d->de_ref)) {
                                goto fail;
                        } else {
                                rcu_read_unlock();
                                return d;
                        }
                }
        }
fail:
        rcu_read_unlock();
        return NULL;
}
EXPORT_SYMBOL_GPL(pnfs_find_get_deviceid);

/*
 * Add a deviceid to the cache.
 * GETDEVICEINFOs for same deviceid can race. If deviceid is found, discard new
 */
struct pnfs_deviceid_node *
pnfs_add_deviceid(struct pnfs_deviceid_cache *c, struct pnfs_deviceid_node *new)
{
        struct pnfs_deviceid_node *d;
        long hash = nfs4_deviceid_hash(&new->de_id);

        dprintk("--> %s hash %ld\n", __func__, hash);
        spin_lock(&c->dc_lock);
        d = pnfs_find_get_deviceid(c, &new->de_id);
        if (d) {
                spin_unlock(&c->dc_lock);
                dprintk("%s [discard]\n", __func__);
                c->dc_free_callback(new);
                return d;
        }
        INIT_HLIST_NODE(&new->de_node);
        atomic_set(&new->de_ref, 1);
        hlist_add_head_rcu(&new->de_node, &c->dc_deviceids[hash]);
        spin_unlock(&c->dc_lock);
        dprintk("%s [new]\n", __func__);
        return new;
}
EXPORT_SYMBOL_GPL(pnfs_add_deviceid);

void
pnfs_put_deviceid_cache(struct nfs_client *clp)
{
        struct pnfs_deviceid_cache *local = clp->cl_devid_cache;

        dprintk("--> %s cl_devid_cache %p\n", __func__, clp->cl_devid_cache);
        if (atomic_dec_and_lock(&local->dc_ref, &clp->cl_lock)) {
                int i;
                /* Verify cache is empty */
                for (i = 0; i < NFS4_DEVICE_ID_HASH_SIZE; i++)
                        BUG_ON(!hlist_empty(&local->dc_deviceids[i]));
                clp->cl_devid_cache = NULL;
                spin_unlock(&clp->cl_lock);
                kfree(local);
        }
}
EXPORT_SYMBOL_GPL(pnfs_put_deviceid_cache);