btrfs: sanity mount option parsing and early mount code

Also adds lots of comments to describe what's going on here.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 136 insertions, 105 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 39bb86945ed0..288300fa5848 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -108,15 +108,18 @@ u64 btrfs_parse_size(char *str)
         return res;
 }
 
-int btrfs_parse_options(char *options, struct btrfs_root *root,
-                        char **subvol_name)
+/*
+ * Regular mount options parser.  Everything that is needed only when
+ * reading in a new superblock is parsed here.
+ */
+int btrfs_parse_options(struct btrfs_root *root, char *options)
 {
-        char * p;
-        struct btrfs_fs_info *info = NULL;
+        struct btrfs_fs_info *info = root->fs_info;
         substring_t args[MAX_OPT_ARGS];
+        char *p, *num;
 
         if (!options)
-                return 1;
+                return 0;
 
         /*
          * strsep changes the string, duplicate it because parse_options
@@ -126,10 +129,8 @@ int btrfs_parse_options(char *options, struct btrfs_root *root,
         if (!options)
                 return -ENOMEM;
 
-        if (root)
-                info = root->fs_info;
 
-        while ((p = strsep (&options, ",")) != NULL) {
+        while ((p = strsep(&options, ",")) != NULL) {
                 int token;
                 if (!*p)
                         continue;
@@ -137,83 +138,64 @@ int btrfs_parse_options(char *options, struct btrfs_root *root,
                 token = match_token(p, tokens, args);
                 switch (token) {
                 case Opt_degraded:
-                        if (info) {
-                                printk("btrfs: allowing degraded mounts\n");
-                                btrfs_set_opt(info->mount_opt, DEGRADED);
-                        }
+                        printk(KERN_INFO "btrfs: allowing degraded mounts\n");
+                        btrfs_set_opt(info->mount_opt, DEGRADED);
                         break;
                 case Opt_subvol:
-                        if (subvol_name) {
-                                *subvol_name = match_strdup(&args[0]);
-                        }
+                        /*
+                         * This one is parsed by btrfs_parse_early_options
+                         * and can be happily ignored here.
+                         */
                         break;
                 case Opt_nodatasum:
-                        if (info) {
-                                printk("btrfs: setting nodatacsum\n");
-                                btrfs_set_opt(info->mount_opt, NODATASUM);
-                        }
+                        printk(KERN_INFO "btrfs: setting nodatacsum\n");
+                        btrfs_set_opt(info->mount_opt, NODATASUM);
                         break;
                 case Opt_nodatacow:
-                        if (info) {
-                                printk("btrfs: setting nodatacow\n");
-                                btrfs_set_opt(info->mount_opt, NODATACOW);
-                                btrfs_set_opt(info->mount_opt, NODATASUM);
-                        }
+                        printk(KERN_INFO "btrfs: setting nodatacow\n");
+                        btrfs_set_opt(info->mount_opt, NODATACOW);
+                        btrfs_set_opt(info->mount_opt, NODATASUM);
                         break;
                 case Opt_ssd:
-                        if (info) {
-                                printk("btrfs: use ssd allocation scheme\n");
-                                btrfs_set_opt(info->mount_opt, SSD);
-                        }
+                        printk(KERN_INFO "btrfs: use ssd allocation scheme\n");
+                        btrfs_set_opt(info->mount_opt, SSD);
                         break;
                 case Opt_nobarrier:
-                        if (info) {
-                                printk("btrfs: turning off barriers\n");
-                                btrfs_set_opt(info->mount_opt, NOBARRIER);
-                        }
+                        printk(KERN_INFO "btrfs: turning off barriers\n");
+                        btrfs_set_opt(info->mount_opt, NOBARRIER);
                         break;
                 case Opt_max_extent:
-                        if (info) {
-                                char *num = match_strdup(&args[0]);
-                                if (num) {
-                                        info->max_extent =
-                                                btrfs_parse_size(num);
-                                        kfree(num);
-
-                                        info->max_extent = max_t(u64,
-                                                         info->max_extent,
-                                                         root->sectorsize);
-                                        printk("btrfs: max_extent at %Lu\n",
-                                               info->max_extent);
-                                }
+                        num = match_strdup(&args[0]);
+                        if (num) {
+                                info->max_extent = btrfs_parse_size(num);
+                                kfree(num);
+
+                                info->max_extent = max_t(u64,
+                                        info->max_extent, root->sectorsize);
+                                printk(KERN_INFO "btrfs: max_extent at %llu\n",
+                                       info->max_extent);
                         }
                         break;
                 case Opt_max_inline:
-                        if (info) {
-                                char *num = match_strdup(&args[0]);
-                                if (num) {
-                                        info->max_inline =
-                                                btrfs_parse_size(num);
-                                        kfree(num);
-
-                                        info->max_inline = max_t(u64,
-                                                         info->max_inline,
-                                                         root->sectorsize);
-                                        printk("btrfs: max_inline at %Lu\n",
-                                               info->max_inline);
-                                }
+                        num = match_strdup(&args[0]);
+                        if (num) {
+                                info->max_inline = btrfs_parse_size(num);
+                                kfree(num);
+
+                                info->max_inline = max_t(u64,
+                                        info->max_inline, root->sectorsize);
+                                printk(KERN_INFO "btrfs: max_inline at %llu\n",
+                                        info->max_inline);
                         }
                         break;
                 case Opt_alloc_start:
-                        if (info) {
-                                char *num = match_strdup(&args[0]);
-                                if (num) {
-                                        info->alloc_start =
-                                                btrfs_parse_size(num);
-                                        kfree(num);
-                                        printk("btrfs: allocations start at "
-                                               "%Lu\n", info->alloc_start);
-                                }
+                        num = match_strdup(&args[0]);
+                        if (num) {
+                                info->alloc_start = btrfs_parse_size(num);
+                                kfree(num);
+                                printk(KERN_INFO
+                                        "btrfs: allocations start at %llu\n",
+                                        info->alloc_start);
                         }
                         break;
                 default:
@@ -221,7 +203,61 @@ int btrfs_parse_options(char *options, struct btrfs_root *root,
                 }
         }
         kfree(options);
-        return 1;
+        return 0;
+}
+
+/*
+ * Parse mount options that are required early in the mount process.
+ *
+ * All other options will be parsed on much later in the mount process and
+ * only when we need to allocate a new super block.
+ */
+static int btrfs_parse_early_options(const char *options,
+                        char **subvol_name)
+{
+        substring_t args[MAX_OPT_ARGS];
+        char *opts, *p;
+        int error = 0;
+
+        if (!options)
+                goto out;
+
+        /*
+         * strsep changes the string, duplicate it because parse_options
+         * gets called twice
+         */
+        opts = kstrdup(options, GFP_KERNEL);
+        if (!opts)
+                return -ENOMEM;
+
+        while ((p = strsep(&opts, ",")) != NULL) {
+                int token;
+                if (!*p)
+                        continue;
+
+                token = match_token(p, tokens, args);
+                switch (token) {
+                case Opt_subvol:
+                        *subvol_name = match_strdup(&args[0]);
+                        break;
+                default:
+                        break;
+                }
+        }
+
+        kfree(opts);
+ out:
+        /*
+         * If no subvolume name is specified we use the default one.  Allocate
+         * a copy of the string "default" here so that code later in the
+         * mount path doesn't care if it's the default volume or another one.
+         */
+        if (!*subvol_name) {
+                *subvol_name = kstrdup("default", GFP_KERNEL);
+                if (!*subvol_name)
+                        return -ENOMEM;
+        }
+        return error;
 }
 
 static int btrfs_fill_super(struct super_block * sb,
@@ -328,23 +364,33 @@ static int btrfs_test_super(struct super_block *s, void *data)
         return root->fs_info->fs_devices == test_fs_devices;
 }
 
-int btrfs_get_sb_bdev(struct file_system_type *fs_type,
-        int flags, const char *dev_name, void *data,
-        struct vfsmount *mnt, const char *subvol)
+/*
+ * Find a superblock for the given device / mount point.
+ *
+ * Note:  This is based on get_sb_bdev from fs/super.c with a few additions
+ *        for multiple device setup.  Make sure to keep it in sync.
+ */
+static int btrfs_get_sb(struct file_system_type *fs_type, int flags,
+                const char *dev_name, void *data, struct vfsmount *mnt)
 {
+        char *subvol_name = NULL;
         struct block_device *bdev = NULL;
         struct super_block *s;
         struct dentry *root;
         struct btrfs_fs_devices *fs_devices = NULL;
         int error = 0;
 
+        error = btrfs_parse_early_options(data, &subvol_name);
+        if (error)
+                goto error;
+
         error = btrfs_scan_one_device(dev_name, flags, fs_type, &fs_devices);
         if (error)
-                return error;
+                goto error_free_subvol_name;
 
         error = btrfs_open_devices(fs_devices, flags, fs_type);
         if (error)
-                return error;
+                goto error_free_subvol_name;
 
         bdev = fs_devices->latest_bdev;
         btrfs_lock_volumes();
@@ -378,51 +424,36 @@ int btrfs_get_sb_bdev(struct file_system_type *fs_type,
                 s->s_flags |= MS_ACTIVE;
         }
 
-        if (subvol) {
-                root = lookup_one_len(subvol, s->s_root, strlen(subvol));
-                if (IS_ERR(root)) {
-                        up_write(&s->s_umount);
-                        deactivate_super(s);
-                        error = PTR_ERR(root);
-                        goto error;
-                }
-                if (!root->d_inode) {
-                        dput(root);
-                        up_write(&s->s_umount);
-                        deactivate_super(s);
-                        error = -ENXIO;
-                        goto error;
-                }
-        } else {
-                root = dget(s->s_root);
+        root = lookup_one_len(subvol_name, s->s_root, strlen(subvol_name));
+        if (IS_ERR(root)) {
+                up_write(&s->s_umount);
+                deactivate_super(s);
+                error = PTR_ERR(root);
+                goto error;
+        }
+        if (!root->d_inode) {
+                dput(root);
+                up_write(&s->s_umount);
+                deactivate_super(s);
+                error = -ENXIO;
+                goto error;
         }
 
         mnt->mnt_sb = s;
         mnt->mnt_root = root;
+
+        kfree(subvol_name);
         return 0;
 
 error_s:
         error = PTR_ERR(s);
 error_bdev:
         btrfs_close_devices(fs_devices);
+error_free_subvol_name:
+        kfree(subvol_name);
 error:
         return error;
 }
-/* end copy & paste */
-
-static int btrfs_get_sb(struct file_system_type *fs_type,
-        int flags, const char *dev_name, void *data, struct vfsmount *mnt)
-{
-        int ret;
-        char *subvol_name = NULL;
-
-        btrfs_parse_options((char *)data, NULL, &subvol_name);
-        ret = btrfs_get_sb_bdev(fs_type, flags, dev_name, data, mnt,
-                        subvol_name ? subvol_name : "default");
-        if (subvol_name)
-                kfree(subvol_name);
-        return ret;
-}
 
 static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {