conf: simplify lxc_fill_autodev()

This function was way more syscall heavy than it needed to be.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/conf.c b/src/lxc/conf.c
index 9f80af3316a19d62410cb3d6f70dda1c78824aa0..fe30800d779f5a7748bc85aad18421a80c76c81d 100644 (file)
--- a/src/lxc/conf.c
+++ b/src/lxc/conf.c
@@ -1203,28 +1203,28 @@ static int mount_autodev(const char *name, const struct lxc_rootfs *rootfs,
        return 0;
 }
 
-struct lxc_devs {
+struct lxc_device_node {
        const char *name;
-       mode_t mode;
-       int maj;
-       int min;
+       const mode_t mode;
+       const int maj;
+       const int min;
 };
 
-static const struct lxc_devs lxc_devs[] = {
-       { "null",    S_IFCHR | S_IRWXU | S_IRWXG | S_IRWXO, 1, 3 },
-       { "zero",    S_IFCHR | S_IRWXU | S_IRWXG | S_IRWXO, 1, 5 },
+static const struct lxc_device_node lxc_devices[] = {
        { "full",    S_IFCHR | S_IRWXU | S_IRWXG | S_IRWXO, 1, 7 },
-       { "urandom", S_IFCHR | S_IRWXU | S_IRWXG | S_IRWXO, 1, 9 },
+       { "null",    S_IFCHR | S_IRWXU | S_IRWXG | S_IRWXO, 1, 3 },
        { "random",  S_IFCHR | S_IRWXU | S_IRWXG | S_IRWXO, 1, 8 },
        { "tty",     S_IFCHR | S_IRWXU | S_IRWXG | S_IRWXO, 5, 0 },
+       { "urandom", S_IFCHR | S_IRWXU | S_IRWXG | S_IRWXO, 1, 9 },
+       { "zero",    S_IFCHR | S_IRWXU | S_IRWXG | S_IRWXO, 1, 5 },
 };
 
 static int lxc_fill_autodev(const struct lxc_rootfs *rootfs)
 {
-       int ret;
+       int i, ret;
        char path[MAXPATHLEN];
-       int i;
        mode_t cmask;
+       bool can_mknod = true;
 
        ret = snprintf(path, MAXPATHLEN, "%s/dev",
                       rootfs->path ? rootfs->mount : "");
@@ -1238,53 +1238,55 @@ static int lxc_fill_autodev(const struct lxc_rootfs *rootfs)
        INFO("Populating \"/dev\"");
 
        cmask = umask(S_IXUSR | S_IXGRP | S_IXOTH);
-       for (i = 0; i < sizeof(lxc_devs) / sizeof(lxc_devs[0]); i++) {
-               const struct lxc_devs *d = &lxc_devs[i];
+       for (i = 0; i < sizeof(lxc_devices) / sizeof(lxc_devices[0]); i++) {
+               char hostpath[MAXPATHLEN];
+               const struct lxc_device_node *device = &lxc_devices[i];
 
                ret = snprintf(path, MAXPATHLEN, "%s/dev/%s",
-                              rootfs->path ? rootfs->mount : "", d->name);
+                              rootfs->path ? rootfs->mount : "", device->name);
                if (ret < 0 || ret >= MAXPATHLEN)
                        return -1;
 
-               ret = mknod(path, d->mode, makedev(d->maj, d->min));
-               if (ret < 0) {
-                       FILE *pathfile;
-                       char hostpath[MAXPATHLEN];
-
-                       if (errno == EEXIST) {
-                               DEBUG("\"%s\" device already existed", path);
+               if (can_mknod) {
+                       ret = mknod(path, device->mode, makedev(device->maj, device->min));
+                       if (ret == 0 || (ret < 0 && errno == EEXIST)) {
+                               DEBUG("Created device node \"%s\"", path);
                                continue;
                        }
 
-                       /* Unprivileged containers cannot create devices, so
-                        * bind mount the device from the host.
-                        */
-                       ret = snprintf(hostpath, MAXPATHLEN, "/dev/%s", d->name);
-                       if (ret < 0 || ret >= MAXPATHLEN)
-                               return -1;
-
-                       pathfile = fopen(path, "wb");
-                       if (!pathfile) {
-                               SYSERROR("Failed to create file \"%s\"", path);
+                       if (errno != EPERM) {
+                               SYSERROR("Failed to create device node \"%s\"", path);
                                return -1;
                        }
-                       fclose(pathfile);
 
-                       ret = safe_mount(hostpath, path, 0, MS_BIND, NULL,
-                                        rootfs->path ? rootfs->mount : NULL);
-                       if (ret < 0) {
-                               SYSERROR("Failed to bind mount \"%s\" from "
-                                        "host into container",
-                                        d->name);
-                               return -1;
-                       }
-                       DEBUG("Bind mounted \"%s\" onto \"%s\"", hostpath,
-                             path);
-               } else {
-                       DEBUG("Created device node \"%s\"", path);
+                       /* This can e.g. happen when the container is
+                        * unprivileged or CAP_MKNOD has been dropped.
+                        */
+                       can_mknod = false;
+               }
+
+               ret = mknod(path, S_IFREG, 0);
+               if (ret < 0 && errno != EEXIST) {
+                       SYSERROR("Failed to create file \"%s\"", path);
+                       return -1;
+               }
+
+               /* Fallback to bind-mounting the device from the host. */
+               ret = snprintf(hostpath, MAXPATHLEN, "/dev/%s", device->name);
+               if (ret < 0 || ret >= MAXPATHLEN)
+                       return -1;
+
+               ret = safe_mount(hostpath, path, 0, MS_BIND, NULL,
+                                rootfs->path ? rootfs->mount : NULL);
+               if (ret < 0) {
+                       SYSERROR("Failed to bind mount host device node \"%s\" "
+                                "onto \"%s\"", hostpath, path);
+                       return -1;
                }
+               DEBUG("Bind mounted host device node \"%s\" onto \"%s\"",
+                     hostpath, path);
        }
-       umask(cmask);
+       (void)umask(cmask);
 
        INFO("Populated \"/dev\"");
        return 0;