Re: [PATCH 2/3] Btrfs: unify subvol= and subvolid= mounting
From: Qu Wenruo
Date: Wed Apr 08 2015 - 02:06:32 EST
-------- Original Message --------
Subject: [PATCH 2/3] Btrfs: unify subvol= and subvolid= mounting
From: Omar Sandoval <osandov@xxxxxxxxxxx>
To: Chris Mason <clm@xxxxxx>, Josef Bacik <jbacik@xxxxxx>, David Sterba
<dsterba@xxxxxxx>, <linux-btrfs@xxxxxxxxxxxxxxx>
Date: 2015å04æ08æ 13:34
Currently, mounting a subvolume with subvolid= takes a different code
path than mounting with subvol=. This isn't really a big deal except for
the fact that mounts done with subvolid= or the default subvolume don't
have a dentry that's connected to the dentry tree like in the subvol=
case. To unify the code paths, when given subvolid= or using the default
subvolume ID, translate it into a subvolume name by walking
ROOT_BACKREFs in the root tree and INODE_REFs in the filesystem trees.
Oh, this patch is what I have tried long long ago, and want to do the
same thing, to show subvolume mount for btrfs.
But it came to me that, superblock->show_path() is a better method to do it.
You can implement btrfs_show_path() to allow mountinfo to get the
subvolume name from subvolid, and don't change the mount routine much.
Thanks,
Qu
Signed-off-by: Omar Sandoval <osandov@xxxxxxxxxxx>
---
fs/btrfs/super.c | 347 ++++++++++++++++++++++++++++++++++++-------------------
1 file changed, 225 insertions(+), 122 deletions(-)
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d38be09..5ab9801 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -841,33 +841,153 @@ out:
return error;
}
-static struct dentry *get_default_root(struct super_block *sb,
- u64 subvol_objectid)
+static char *get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
+ u64 subvol_objectid)
{
- struct btrfs_fs_info *fs_info = btrfs_sb(sb);
struct btrfs_root *root = fs_info->tree_root;
- struct btrfs_root *new_root;
- struct btrfs_dir_item *di;
- struct btrfs_path *path;
- struct btrfs_key location;
- struct inode *inode;
- u64 dir_id;
- int new = 0;
+ struct btrfs_root *fs_root;
+ struct btrfs_root_ref *root_ref;
+ struct btrfs_inode_ref *inode_ref;
+ struct btrfs_key key;
+ struct btrfs_path *path = NULL;
+ char *name = NULL, *ptr;
+ u64 dirid;
+ int len;
+ int ret;
+
+ path = btrfs_alloc_path();
+ if (!path) {
+ ret = -ENOMEM;
+ goto err;
+ }
+ path->leave_spinning = 1;
+
+ name = kmalloc(PATH_MAX, GFP_NOFS);
+ if (!name) {
+ ret = -ENOMEM;
+ goto err;
+ }
+ ptr = name + PATH_MAX - 1;
+ ptr[0] = '\0';
/*
- * We have a specific subvol we want to mount, just setup location and
- * go look up the root.
+ * Walk up the subvolume trees in the tree of tree roots by root
+ * backrefs until we hit the top-level subvolume.
*/
- if (subvol_objectid) {
- location.objectid = subvol_objectid;
- location.type = BTRFS_ROOT_ITEM_KEY;
- location.offset = (u64)-1;
- goto find_root;
+ while (subvol_objectid != BTRFS_FS_TREE_OBJECTID) {
+ key.objectid = subvol_objectid;
+ key.type = BTRFS_ROOT_BACKREF_KEY;
+ key.offset = (u64)-1;
+
+ ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+ if (ret < 0) {
+ goto err;
+ } else if (ret > 0) {
+ ret = btrfs_previous_item(root, path, subvol_objectid,
+ BTRFS_ROOT_BACKREF_KEY);
+ if (ret < 0) {
+ goto err;
+ } else if (ret > 0) {
+ ret = -ENOENT;
+ goto err;
+ }
+ }
+
+ btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+ subvol_objectid = key.offset;
+
+ root_ref = btrfs_item_ptr(path->nodes[0], path->slots[0],
+ struct btrfs_root_ref);
+ len = btrfs_root_ref_name_len(path->nodes[0], root_ref);
+ ptr -= len + 1;
+ if (ptr < name) {
+ ret = -ENAMETOOLONG;
+ goto err;
+ }
+ read_extent_buffer(path->nodes[0], ptr + 1,
+ (unsigned long)(root_ref + 1), len);
+ ptr[0] = '/';
+ dirid = btrfs_root_ref_dirid(path->nodes[0], root_ref);
+ btrfs_release_path(path);
+
+ key.objectid = subvol_objectid;
+ key.type = BTRFS_ROOT_ITEM_KEY;
+ key.offset = (u64)-1;
+ fs_root = btrfs_read_fs_root_no_name(fs_info, &key);
+ if (IS_ERR(fs_root)) {
+ ret = PTR_ERR(fs_root);
+ goto err;
+ }
+
+ /*
+ * Walk up the filesystem tree by inode refs until we hit the
+ * root directory.
+ */
+ while (dirid != BTRFS_FIRST_FREE_OBJECTID) {
+ key.objectid = dirid;
+ key.type = BTRFS_INODE_REF_KEY;
+ key.offset = (u64)-1;
+
+ ret = btrfs_search_slot(NULL, fs_root, &key, path, 0, 0);
+ if (ret < 0) {
+ goto err;
+ } else if (ret > 0) {
+ ret = btrfs_previous_item(fs_root, path, dirid,
+ BTRFS_INODE_REF_KEY);
+ if (ret < 0) {
+ goto err;
+ } else if (ret > 0) {
+ ret = -ENOENT;
+ goto err;
+ }
+ }
+
+ btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+ dirid = key.offset;
+
+ inode_ref = btrfs_item_ptr(path->nodes[0],
+ path->slots[0],
+ struct btrfs_inode_ref);
+ len = btrfs_inode_ref_name_len(path->nodes[0],
+ inode_ref);
+ ptr -= len + 1;
+ if (ptr < name) {
+ ret = -ENAMETOOLONG;
+ goto err;
+ }
+ read_extent_buffer(path->nodes[0], ptr + 1,
+ (unsigned long)(inode_ref + 1), len);
+ ptr[0] = '/';
+ btrfs_release_path(path);
+ }
+ }
+
+ btrfs_free_path(path);
+ if (ptr == name + PATH_MAX - 1) {
+ name[0] = '/';
+ name[1] = '\0';
+ } else {
+ memmove(name, ptr, name + PATH_MAX - ptr);
}
+ return name;
+
+err:
+ btrfs_free_path(path);
+ kfree(name);
+ return ERR_PTR(ret);
+}
+
+static int get_default_subvol_objectid(struct btrfs_fs_info *fs_info, u64 *objectid)
+{
+ struct btrfs_root *root = fs_info->tree_root;
+ struct btrfs_dir_item *di;
+ struct btrfs_path *path;
+ struct btrfs_key location;
+ u64 dir_id;
path = btrfs_alloc_path();
if (!path)
- return ERR_PTR(-ENOMEM);
+ return -ENOMEM;
path->leave_spinning = 1;
/*
@@ -879,49 +999,23 @@ static struct dentry *get_default_root(struct super_block *sb,
di = btrfs_lookup_dir_item(NULL, root, path, dir_id, "default", 7, 0);
if (IS_ERR(di)) {
btrfs_free_path(path);
- return ERR_CAST(di);
+ return PTR_ERR(di);
}
if (!di) {
/*
* Ok the default dir item isn't there. This is weird since
* it's always been there, but don't freak out, just try and
- * mount to root most subvolume.
+ * mount the top-level subvolume.
*/
btrfs_free_path(path);
- dir_id = BTRFS_FIRST_FREE_OBJECTID;
- new_root = fs_info->fs_root;
- goto setup_root;
+ *objectid = BTRFS_FS_TREE_OBJECTID;
+ return 0;
}
btrfs_dir_item_key_to_cpu(path->nodes[0], di, &location);
btrfs_free_path(path);
-
-find_root:
- new_root = btrfs_read_fs_root_no_name(fs_info, &location);
- if (IS_ERR(new_root))
- return ERR_CAST(new_root);
-
- dir_id = btrfs_root_dirid(&new_root->root_item);
-setup_root:
- location.objectid = dir_id;
- location.type = BTRFS_INODE_ITEM_KEY;
- location.offset = 0;
-
- inode = btrfs_iget(sb, &location, new_root, &new);
- if (IS_ERR(inode))
- return ERR_CAST(inode);
-
- /*
- * If we're just mounting the root most subvol put the inode and return
- * a reference to the dentry. We will have already gotten a reference
- * to the inode in btrfs_fill_super so we're good to go.
- */
- if (!new && sb->s_root->d_inode == inode) {
- iput(inode);
- return dget(sb->s_root);
- }
-
- return d_obtain_root(inode);
+ *objectid = location.objectid;
+ return 0;
}
static int btrfs_fill_super(struct super_block *sb,
@@ -1129,109 +1223,123 @@ static inline int is_subvolume_inode(struct inode *inode)
}
/*
- * This will strip out the subvol=%s argument for an argument string and add
- * subvolid=0 to make sure we get the actual tree root for path walking to the
- * subvol we want.
+ * This will add subvolid=0 to the argument string while removing any subvol=
+ * and subvolid= arguments to make sure we get the top-level root for path
+ * walking to the subvol we want.
*/
static char *setup_root_args(char *args)
{
- unsigned len = strlen(args) + 2 + 1;
- char *src, *dst, *buf;
-
- /*
- * We need the same args as before, but with this substitution:
- * s!subvol=[^,]+!subvolid=0!
- *
- * Since the replacement string is up to 2 bytes longer than the
- * original, allocate strlen(args) + 2 + 1 bytes.
- */
+ char *p, *dst, *buf;
- src = strstr(args, "subvol=");
- /* This shouldn't happen, but just in case.. */
- if (!src)
- return NULL;
+ if (!args)
+ return kstrdup("subvolid=0", GFP_NOFS);
- buf = dst = kmalloc(len, GFP_NOFS);
+ /* The worst case is that we add ",subvolid=0" to the end. */
+ buf = dst = kmalloc(strlen(args) + strlen(",subvolid=0") + 1, GFP_NOFS);
if (!buf)
return NULL;
- /*
- * If the subvol= arg is not at the start of the string,
- * copy whatever precedes it into buf.
- */
- if (src != args) {
- *src++ = '\0';
- strcpy(buf, args);
- dst += strlen(args);
+ while (1) {
+ p = strchrnul(args, ',');
+ if (strncmp(args, "subvol=", strlen("subvol=")) != 0 &&
+ strncmp(args, "subvolid=", strlen("subvolid=")) != 0) {
+ memcpy(dst, args, p - args);
+ dst += p - args;
+ *dst++ = ',';
+ }
+ if (*p)
+ args = p + 1;
+ else
+ break;
}
-
strcpy(dst, "subvolid=0");
- dst += strlen("subvolid=0");
-
- /*
- * If there is a "," after the original subvol=... string,
- * copy that suffix into our buffer. Otherwise, we're done.
- */
- src = strchr(src, ',');
- if (src)
- strcpy(dst, src);
return buf;
}
-static struct dentry *mount_subvol(const char *subvol_name, int flags,
- const char *device_name, char *data)
+static struct dentry *mount_subvol(const char *subvol_name, u64 subvol_objectid,
+ int flags, const char *device_name,
+ char *data)
{
struct dentry *root;
- struct vfsmount *mnt;
+ struct vfsmount *mnt = NULL;
char *newargs;
+ int ret;
newargs = setup_root_args(data);
- if (!newargs)
- return ERR_PTR(-ENOMEM);
- mnt = vfs_kern_mount(&btrfs_fs_type, flags, device_name,
- newargs);
+ if (!newargs) {
+ root = ERR_PTR(-ENOMEM);
+ goto out;
+ }
- if (PTR_RET(mnt) == -EBUSY) {
+ mnt = vfs_kern_mount(&btrfs_fs_type, flags, device_name, newargs);
+ if (PTR_ERR_OR_ZERO(mnt) == -EBUSY) {
if (flags & MS_RDONLY) {
- mnt = vfs_kern_mount(&btrfs_fs_type, flags & ~MS_RDONLY, device_name,
- newargs);
+ mnt = vfs_kern_mount(&btrfs_fs_type, flags & ~MS_RDONLY,
+ device_name, newargs);
} else {
- int r;
- mnt = vfs_kern_mount(&btrfs_fs_type, flags | MS_RDONLY, device_name,
- newargs);
+ mnt = vfs_kern_mount(&btrfs_fs_type, flags | MS_RDONLY,
+ device_name, newargs);
if (IS_ERR(mnt)) {
- kfree(newargs);
- return ERR_CAST(mnt);
+ root = ERR_CAST(mnt);
+ mnt = NULL;
+ goto out;
}
down_write(&mnt->mnt_sb->s_umount);
- r = btrfs_remount(mnt->mnt_sb, &flags, NULL);
+ ret = btrfs_remount(mnt->mnt_sb, &flags, NULL);
up_write(&mnt->mnt_sb->s_umount);
- if (r < 0) {
- /* FIXME: release vfsmount mnt ??*/
- kfree(newargs);
- return ERR_PTR(r);
+ if (ret < 0) {
+ root = ERR_PTR(ret);
+ goto out;
}
}
}
+ if (IS_ERR(mnt)) {
+ root = ERR_CAST(mnt);
+ mnt = NULL;
+ goto out;
+ }
- kfree(newargs);
+ if (!subvol_name) {
+ if (!subvol_objectid) {
+ ret = get_default_subvol_objectid(btrfs_sb(mnt->mnt_sb),
+ &subvol_objectid);
+ if (ret) {
+ root = ERR_PTR(ret);
+ goto out;
+ }
+ }
+ subvol_name = get_subvol_name_from_objectid(btrfs_sb(mnt->mnt_sb),
+ subvol_objectid);
+ if (IS_ERR(subvol_name)) {
+ root = ERR_CAST(subvol_name);
+ subvol_name = NULL;
+ goto out;
+ }
- if (IS_ERR(mnt))
- return ERR_CAST(mnt);
+ }
root = mount_subtree(mnt, subvol_name);
+ mnt = NULL; /* mount_subtree drops our reference on the vfsmount. */
if (!IS_ERR(root) && !is_subvolume_inode(root->d_inode)) {
struct super_block *s = root->d_sb;
dput(root);
root = ERR_PTR(-EINVAL);
deactivate_locked_super(s);
- printk(KERN_ERR "BTRFS: '%s' is not a valid subvolume\n",
- subvol_name);
+ pr_err("BTRFS: '%s' is not a valid subvolume\n", subvol_name);
+ }
+ if (!IS_ERR(root) && subvol_objectid &&
+ BTRFS_I(root->d_inode)->root->root_key.objectid != subvol_objectid) {
+ pr_warn("BTRFS: subvol '%s' does not match subvolid %llu\n",
+ subvol_name, subvol_objectid);
}
+out:
+ mntput(mnt);
+ kfree(newargs);
+ kfree(subvol_name);
return root;
}
@@ -1296,7 +1404,6 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
{
struct block_device *bdev = NULL;
struct super_block *s;
- struct dentry *root;
struct btrfs_fs_devices *fs_devices = NULL;
struct btrfs_fs_info *fs_info = NULL;
struct security_mnt_opts new_sec_opts;
@@ -1316,10 +1423,10 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
return ERR_PTR(error);
}
- if (subvol_name) {
- root = mount_subvol(subvol_name, flags, device_name, data);
- kfree(subvol_name);
- return root;
+ if (subvol_name || subvol_objectid != BTRFS_FS_TREE_OBJECTID) {
+ /* mount_subvol() will free subvol_name. */
+ return mount_subvol(subvol_name, subvol_objectid, flags,
+ device_name, data);
}
security_init_mnt_opts(&new_sec_opts);
@@ -1385,23 +1492,19 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
error = btrfs_fill_super(s, fs_devices, data,
flags & MS_SILENT ? 1 : 0);
}
-
- root = !error ? get_default_root(s, subvol_objectid) : ERR_PTR(error);
- if (IS_ERR(root)) {
+ if (error) {
deactivate_locked_super(s);
- error = PTR_ERR(root);
goto error_sec_opts;
}
fs_info = btrfs_sb(s);
error = setup_security_options(fs_info, s, &new_sec_opts);
if (error) {
- dput(root);
deactivate_locked_super(s);
goto error_sec_opts;
}
- return root;
+ return dget(s->s_root);
error_close_devices:
btrfs_close_devices(fs_devices);
--
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