[PATCH v3 0/4] btrfs: cleanup mount path

[PATCH v3 0/4] btrfs: cleanup mount path

[Misono, Tomohiro]

Summary:
Cleanup mount path by avoiding calling btrfs_mount() twice.
No functional change. See below for longer explanation.

Changelog:
v3:
  Reorganized patches again into four and added comments to the source.
  Each patch can be applied and compiled while maintaining functionality.
  The first one is the preparation and the second one is the main part.
  The last two are small cleanups.

v2:
  Split the patch into three parts.

Tomohiro Misono (4):
  btrfs: add mount_root() and new file_system_type
  btrfs: cleanup btrfs_mount() using mount_root()
  btrfs: split parse_early_options() in two
  btrfs: remove unused setup_root_args()

 fs/btrfs/super.c | 252 ++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 149 insertions(+), 103 deletions(-)

====================
Background Explanation:
btrfs uses mount_subtree() to mount a subvolume directly.  This function
needs a vfsmount* of device's root (/), which is a return value of
vfs_kern_mount() (therefore root has to be mounted internally anyway).

Current approach of getting root's vfsmount* in mount time is a bit tricky:
0. VFS layer calls vfs_kern_mount() with registered file_system_type
   (for btrfs, btrfs_fs_type). btrfs_mount() is called on the way.
1. btrfs_parse_early_options() parses "subvolid=" mount option and set the
   value to subvol_objectid. Otherwise, subvol_objectid has the initial
   value of 0
2. check subvol_objectid is 5 or not. This time id is not 5, and
   btrfs_mount() returns by calling mount_subvol()
3. In mount_subvol(), original mount options are modified to contain
   "subvolid=0" in setup_root_args(). Then, vfs_kern_mount() is called with
   btrfs_fs_type and new options
4. btrfs_mount() is called again
5. btrfs_parse_early_options() parses "subvolid=0" and set 5 (instead of 0)
   to subvol_objectid
6. check subvol_objectid is 5 or not. This time id is 5 and mount_subvol()
   is not called. btrfs_mount() finishes mounting a root
7. (in mount_subvol()) with using a return vale of vfs_kern_mount(), it
   calls mount_subtree()
8 return subvolume's dentry

As illustrated above, calling btrfs_mount() twice complicates the problem.
We can use another file_system_type (which has different callback
function to mount root) for arguments of our vfs_kern_mount() call to 
avoid this.

In this approach: 
1. parse subvol id related options for later use in mount_subvol()
2. mount device's root by calling vfs_kern_mount() with
   different file_system_type
3. return by calling mount_subvol()

I think this approach is the same as nfsv4, which is the only other
filesystem using mount_subtree() currently, and easy to understand.

Most of the change is done by just reorganizing the original code of
btrfs_mount()/mount_subvol() into btrfs_mount()/mount_subvol()/mount_root()

btrfs_parse_early_options() is split into two parts to avoid "device="
option will be handled twice (though it cause no harm). setup_root_args()
is deleted as not needed anymore.

-- 
2.9.5

[PATCH 1/4] btrfs: add mount_root() and new file_system_type

[Misono, Tomohiro]

Add mount_root() and new file_system_type for preparation of cleanup of
btrfs_mount(). Code path is not changed yet.

mount_root() is almost the same as current btrfs_mount(), but doesn't
have subvolume related part.

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
---
 fs/btrfs/super.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 12540b6..fe43606 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -66,6 +66,7 @@
 
 static const struct super_operations btrfs_super_ops;
 static struct file_system_type btrfs_fs_type;
+static struct file_system_type btrfs_root_fs_type;
 
 static int btrfs_remount(struct super_block *sb, int *flags, char *data);
 
@@ -1514,6 +1515,112 @@ static int setup_security_options(struct btrfs_fs_info *fs_info,
 	return ret;
 }
 
+static struct dentry *mount_root(struct file_system_type *fs_type, int flags,
+		const char *device_name, void *data)
+{
+	struct block_device *bdev = NULL;
+	struct super_block *s;
+	struct btrfs_fs_devices *fs_devices = NULL;
+	struct btrfs_fs_info *fs_info = NULL;
+	struct security_mnt_opts new_sec_opts;
+	fmode_t mode = FMODE_READ;
+	char *subvol_name = NULL;
+	u64 subvol_objectid = 0;
+	int error = 0;
+
+	if (!(flags & MS_RDONLY))
+		mode |= FMODE_WRITE;
+
+	error = btrfs_parse_early_options(data, mode, fs_type,
+					  &subvol_name, &subvol_objectid,
+					  &fs_devices);
+	if (error) {
+		kfree(subvol_name);
+		return ERR_PTR(error);
+	}
+
+	security_init_mnt_opts(&new_sec_opts);
+	if (data) {
+		error = parse_security_options(data, &new_sec_opts);
+		if (error)
+			return ERR_PTR(error);
+	}
+
+	error = btrfs_scan_one_device(device_name, mode, fs_type, &fs_devices);
+	if (error)
+		goto error_sec_opts;
+
+	/*
+	 * Setup a dummy root and fs_info for test/set super.  This is because
+	 * we don't actually fill this stuff out until open_ctree, but we need
+	 * it for searching for existing supers, so this lets us do that and
+	 * then open_ctree will properly initialize everything later.
+	 */
+	fs_info = kzalloc(sizeof(struct btrfs_fs_info), GFP_NOFS);
+	if (!fs_info) {
+		error = -ENOMEM;
+		goto error_sec_opts;
+	}
+
+	fs_info->fs_devices = fs_devices;
+
+	fs_info->super_copy = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);
+	fs_info->super_for_commit = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);
+	security_init_mnt_opts(&fs_info->security_opts);
+	if (!fs_info->super_copy || !fs_info->super_for_commit) {
+		error = -ENOMEM;
+		goto error_fs_info;
+	}
+
+	error = btrfs_open_devices(fs_devices, mode, fs_type);
+	if (error)
+		goto error_fs_info;
+
+	if (!(flags & MS_RDONLY) && fs_devices->rw_devices == 0) {
+		error = -EACCES;
+		goto error_close_devices;
+	}
+
+	bdev = fs_devices->latest_bdev;
+	s = sget(fs_type, btrfs_test_super, btrfs_set_super, flags | MS_NOSEC,
+		 fs_info);
+	if (IS_ERR(s)) {
+		error = PTR_ERR(s);
+		goto error_close_devices;
+	}
+
+	if (s->s_root) {
+		btrfs_close_devices(fs_devices);
+		free_fs_info(fs_info);
+		if ((flags ^ s->s_flags) & MS_RDONLY)
+			error = -EBUSY;
+	} else {
+		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
+		btrfs_sb(s)->bdev_holder = fs_type;
+		error = btrfs_fill_super(s, fs_devices, data);
+	}
+	if (error) {
+		deactivate_locked_super(s);
+		goto error_sec_opts;
+	}
+
+	fs_info = btrfs_sb(s);
+	error = setup_security_options(fs_info, s, &new_sec_opts);
+	if (error) {
+		deactivate_locked_super(s);
+		goto error_sec_opts;
+	}
+
+	return dget(s->s_root);
+
+error_close_devices:
+	btrfs_close_devices(fs_devices);
+error_fs_info:
+	free_fs_info(fs_info);
+error_sec_opts:
+	security_free_mnt_opts(&new_sec_opts);
+	return ERR_PTR(error);
+}
 /*
  * Find a superblock for the given device / mount point.
  *
@@ -2133,6 +2240,15 @@ static struct file_system_type btrfs_fs_type = {
 	.kill_sb	= btrfs_kill_super,
 	.fs_flags	= FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA,
 };
+
+static struct file_system_type btrfs_root_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "btrfs",
+	.mount		= mount_root,
+	.kill_sb	= btrfs_kill_super,
+	.fs_flags	= FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA,
+};
+
 MODULE_ALIAS_FS("btrfs");
 
 static int btrfs_control_open(struct inode *inode, struct file *file)
-- 
2.9.5

Re: [PATCH 1/4] btrfs: add mount_root() and new file_system_type

[David Sterba]

On Mon, Sep 25, 2017 at 04:27:07PM +0900, Misono, Tomohiro wrote:
> Add mount_root() and new file_system_type for preparation of cleanup of
> btrfs_mount(). Code path is not changed yet.
> 
> mount_root() is almost the same as current btrfs_mount(), but doesn't
> have subvolume related part.
> 
> Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
> ---
>  fs/btrfs/super.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 116 insertions(+)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 12540b6..fe43606 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -66,6 +66,7 @@
>  
>  static const struct super_operations btrfs_super_ops;
>  static struct file_system_type btrfs_fs_type;
> +static struct file_system_type btrfs_root_fs_type;

A comment why we need this would be useful.

>  
>  static int btrfs_remount(struct super_block *sb, int *flags, char *data);
>  
> @@ -1514,6 +1515,112 @@ static int setup_security_options(struct btrfs_fs_info *fs_info,
>  	return ret;
>  }
>  
> +static struct dentry *mount_root(struct file_system_type *fs_type, int flags,

'mount_root' is too generic and could be confused with other mount_*
functions from VFS, btrfs_mount_root would be better.

> +		const char *device_name, void *data)
> +{
> +	struct block_device *bdev = NULL;
> +	struct super_block *s;
> +	struct btrfs_fs_devices *fs_devices = NULL;
> +	struct btrfs_fs_info *fs_info = NULL;
> +	struct security_mnt_opts new_sec_opts;
> +	fmode_t mode = FMODE_READ;
> +	char *subvol_name = NULL;
> +	u64 subvol_objectid = 0;
> +	int error = 0;
> +
> +	if (!(flags & MS_RDONLY))
> +		mode |= FMODE_WRITE;
> +
> +	error = btrfs_parse_early_options(data, mode, fs_type,
> +					  &subvol_name, &subvol_objectid,
> +					  &fs_devices);
> +	if (error) {
> +		kfree(subvol_name);
> +		return ERR_PTR(error);
> +	}
> +
> +	security_init_mnt_opts(&new_sec_opts);
> +	if (data) {
> +		error = parse_security_options(data, &new_sec_opts);
> +		if (error)
> +			return ERR_PTR(error);
> +	}
> +
> +	error = btrfs_scan_one_device(device_name, mode, fs_type, &fs_devices);
> +	if (error)
> +		goto error_sec_opts;
> +
> +	/*
> +	 * Setup a dummy root and fs_info for test/set super.  This is because
> +	 * we don't actually fill this stuff out until open_ctree, but we need
> +	 * it for searching for existing supers, so this lets us do that and
> +	 * then open_ctree will properly initialize everything later.
> +	 */
> +	fs_info = kzalloc(sizeof(struct btrfs_fs_info), GFP_NOFS);

Why GFP_NOFS?

> +	if (!fs_info) {
> +		error = -ENOMEM;
> +		goto error_sec_opts;
> +	}
> +
> +	fs_info->fs_devices = fs_devices;
> +
> +	fs_info->super_copy = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);
> +	fs_info->super_for_commit = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);

Also here. Current code uses GFP_KERNEL so this might got switched in
the meantim.

> +	security_init_mnt_opts(&fs_info->security_opts);
> +	if (!fs_info->super_copy || !fs_info->super_for_commit) {
> +		error = -ENOMEM;
> +		goto error_fs_info;
> +	}
> +
> +	error = btrfs_open_devices(fs_devices, mode, fs_type);
> +	if (error)
> +		goto error_fs_info;
> +
> +	if (!(flags & MS_RDONLY) && fs_devices->rw_devices == 0) {
> +		error = -EACCES;
> +		goto error_close_devices;
> +	}
> +
> +	bdev = fs_devices->latest_bdev;
> +	s = sget(fs_type, btrfs_test_super, btrfs_set_super, flags | MS_NOSEC,
> +		 fs_info);
> +	if (IS_ERR(s)) {
> +		error = PTR_ERR(s);
> +		goto error_close_devices;
> +	}
> +
> +	if (s->s_root) {
> +		btrfs_close_devices(fs_devices);
> +		free_fs_info(fs_info);
> +		if ((flags ^ s->s_flags) & MS_RDONLY)
> +			error = -EBUSY;
> +	} else {
> +		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
> +		btrfs_sb(s)->bdev_holder = fs_type;
> +		error = btrfs_fill_super(s, fs_devices, data);
> +	}
> +	if (error) {
> +		deactivate_locked_super(s);
> +		goto error_sec_opts;
> +	}
> +
> +	fs_info = btrfs_sb(s);
> +	error = setup_security_options(fs_info, s, &new_sec_opts);
> +	if (error) {
> +		deactivate_locked_super(s);
> +		goto error_sec_opts;
> +	}
> +
> +	return dget(s->s_root);
> +
> +error_close_devices:
> +	btrfs_close_devices(fs_devices);
> +error_fs_info:
> +	free_fs_info(fs_info);
> +error_sec_opts:
> +	security_free_mnt_opts(&new_sec_opts);
> +	return ERR_PTR(error);
> +}
>  /*
>   * Find a superblock for the given device / mount point.
>   *
> @@ -2133,6 +2240,15 @@ static struct file_system_type btrfs_fs_type = {
>  	.kill_sb	= btrfs_kill_super,
>  	.fs_flags	= FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA,
>  };
> +
> +static struct file_system_type btrfs_root_fs_type = {
> +	.owner		= THIS_MODULE,
> +	.name		= "btrfs",
> +	.mount		= mount_root,
> +	.kill_sb	= btrfs_kill_super,
> +	.fs_flags	= FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA,
> +};
> +
>  MODULE_ALIAS_FS("btrfs");
>  
>  static int btrfs_control_open(struct inode *inode, struct file *file)
> -- 
> 2.9.5
> 
> --
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> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

[PATCH 2/4] btrfs: cleanup btrfs_mount() using mount_root()

[Misono, Tomohiro]

Cleanups btrfs_mount() by using mount_root(). This avoids getting
btrfs_mount() called twice in mount path.

Old btrfs_mount() will do:
0. VFS layer calls vfs_kern_mount() with registered file_system_type
   (for btrfs, btrfs_fs_type). btrfs_mount() is called on the way.
1. btrfs_parse_early_options() parses "subvolid=" mount option and set the
   value to subvol_objectid. Otherwise, subvol_objectid has the initial
    value of 0
2. check subvol_objectid is 5 or not. This time id is not 5, and
   btrfs_mount() returns by calling mount_subvol()
3. In mount_subvol(), original mount options are modified to contain
   "subvolid=0" in setup_root_args(). Then, vfs_kern_mount() is called with
   btrfs_fs_type and new options
4. btrfs_mount() is called again
5. btrfs_parse_early_options() parses "subvolid=0" and set 5 (instead of 0)
   to subvol_objectid
6. check subvol_objectid is 5 or not. This time id is 5 and mount_subvol()
   is not called. btrfs_mount() finishes mounting a root
7. (in mount_subvol()) with using a return vale of vfs_kern_mount(), it
   calls mount_subtree()
8 return subvolume's dentry

Reusing the same file_system_type (and btrfs_mount()) for vfs_kern_mount()
is the cause of complication.

Instead, new btrfs_mount() will do:
1. parse subvol id related options for later use in mount_subvol()
2. mount device's root by calling vfs_kern_mount() with
   btrfs_root_fs_type, which is not registered to VFS by
	 register_filesystem(). As a result, mount_root() is called
3. return by calling mount_subvol()

The code of 2. is moved from the first part of mount_subvol().

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
---
 fs/btrfs/super.c | 186 +++++++++++++++++--------------------------------------
 1 file changed, 58 insertions(+), 128 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index fe43606..1c34ca6 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1363,48 +1363,11 @@ static char *setup_root_args(char *args)
 
 static struct dentry *mount_subvol(const char *subvol_name, u64 subvol_objectid,
 				   int flags, const char *device_name,
-				   char *data)
+				   char *data, struct vfsmount *mnt)
 {
 	struct dentry *root;
-	struct vfsmount *mnt = NULL;
-	char *newargs;
 	int ret;
 
-	newargs = setup_root_args(data);
-	if (!newargs) {
-		root = ERR_PTR(-ENOMEM);
-		goto out;
-	}
-
-	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);
-		} else {
-			mnt = vfs_kern_mount(&btrfs_fs_type, flags | MS_RDONLY,
-					     device_name, newargs);
-			if (IS_ERR(mnt)) {
-				root = ERR_CAST(mnt);
-				mnt = NULL;
-				goto out;
-			}
-
-			down_write(&mnt->mnt_sb->s_umount);
-			ret = btrfs_remount(mnt->mnt_sb, &flags, NULL);
-			up_write(&mnt->mnt_sb->s_umount);
-			if (ret < 0) {
-				root = ERR_PTR(ret);
-				goto out;
-			}
-		}
-	}
-	if (IS_ERR(mnt)) {
-		root = ERR_CAST(mnt);
-		mnt = NULL;
-		goto out;
-	}
-
 	if (!subvol_name) {
 		if (!subvol_objectid) {
 			ret = get_default_subvol_objectid(btrfs_sb(mnt->mnt_sb),
@@ -1460,7 +1423,6 @@ static struct dentry *mount_subvol(const char *subvol_name, u64 subvol_objectid,
 
 out:
 	mntput(mnt);
-	kfree(newargs);
 	kfree(subvol_name);
 	return root;
 }
@@ -1515,6 +1477,12 @@ static int setup_security_options(struct btrfs_fs_info *fs_info,
 	return ret;
 }
 
+/*
+ * Find a superblock for the given device / mount point.
+ *
+ * Note:  This is based on mount_bdev from fs/super.c with a few additions
+ *	  for multiple device setup.  Make sure to keep it in sync.
+ */
 static struct dentry *mount_root(struct file_system_type *fs_type, int flags,
 		const char *device_name, void *data)
 {
@@ -1621,20 +1589,34 @@ static struct dentry *mount_root(struct file_system_type *fs_type, int flags,
 	security_free_mnt_opts(&new_sec_opts);
 	return ERR_PTR(error);
 }
+
 /*
- * Find a superblock for the given device / mount point.
+ * Mount function which is called by VFS layer.
  *
- * 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.
+ * In order to allow mounting a subvolume directly, btrfs uses
+ * mount_subtree() which needs vfsmount* of device's root (/).
+ * This means device's root has to be mounted internally in any case.
+ *
+ * Operation flow:
+ *   1. Parse subvol id related options for later use in mount_subvol().
+ *
+ *   2. Mount device's root (/) by calling vfs_kern_mount().
+ *
+ *      NOTE: vfs_kern_mount() is used by VFS to call btrfs_mount() in the
+ *      first place. In order to avoid calling btrfs_mount() again, we use
+ *      different file_system_type which is not registered to VFS by
+ *      register_filesystem(). As a result, mount_root() is called.
+ *      The return value will be used by mount_subtree() in mount_subvol().
+ *
+ *   3. Call mount_subvol() to get the dentry of subvolume. Since there is
+ *      "btrfs subvolume set-default", mount_subvol() is called always.
  */
 static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 		const char *device_name, void *data)
 {
-	struct block_device *bdev = NULL;
-	struct super_block *s;
 	struct btrfs_fs_devices *fs_devices = NULL;
-	struct btrfs_fs_info *fs_info = NULL;
-	struct security_mnt_opts new_sec_opts;
+	struct vfsmount *mnt_root;
+	struct dentry *root;
 	fmode_t mode = FMODE_READ;
 	char *subvol_name = NULL;
 	u64 subvol_objectid = 0;
@@ -1651,93 +1633,41 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 		return ERR_PTR(error);
 	}
 
-	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);
-	if (data) {
-		error = parse_security_options(data, &new_sec_opts);
-		if (error)
-			return ERR_PTR(error);
-	}
-
-	error = btrfs_scan_one_device(device_name, mode, fs_type, &fs_devices);
-	if (error)
-		goto error_sec_opts;
-
-	/*
-	 * Setup a dummy root and fs_info for test/set super.  This is because
-	 * we don't actually fill this stuff out until open_ctree, but we need
-	 * it for searching for existing supers, so this lets us do that and
-	 * then open_ctree will properly initialize everything later.
-	 */
-	fs_info = kzalloc(sizeof(struct btrfs_fs_info), GFP_NOFS);
-	if (!fs_info) {
-		error = -ENOMEM;
-		goto error_sec_opts;
-	}
-
-	fs_info->fs_devices = fs_devices;
-
-	fs_info->super_copy = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);
-	fs_info->super_for_commit = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);
-	security_init_mnt_opts(&fs_info->security_opts);
-	if (!fs_info->super_copy || !fs_info->super_for_commit) {
-		error = -ENOMEM;
-		goto error_fs_info;
-	}
-
-	error = btrfs_open_devices(fs_devices, mode, fs_type);
-	if (error)
-		goto error_fs_info;
-
-	if (!(flags & MS_RDONLY) && fs_devices->rw_devices == 0) {
-		error = -EACCES;
-		goto error_close_devices;
-	}
-
-	bdev = fs_devices->latest_bdev;
-	s = sget(fs_type, btrfs_test_super, btrfs_set_super, flags | MS_NOSEC,
-		 fs_info);
-	if (IS_ERR(s)) {
-		error = PTR_ERR(s);
-		goto error_close_devices;
-	}
+	/* mount device's root (/) */
+	mnt_root = vfs_kern_mount(&btrfs_root_fs_type, flags, device_name, data);
+	if (PTR_ERR_OR_ZERO(mnt_root) == -EBUSY) {
+		if (flags & MS_RDONLY) {
+			mnt_root = vfs_kern_mount(&btrfs_root_fs_type, flags & ~MS_RDONLY,
+					     device_name, data);
+		} else {
+			mnt_root = vfs_kern_mount(&btrfs_root_fs_type, flags | MS_RDONLY,
+					     device_name, data);
+			if (IS_ERR(mnt_root)) {
+				root = ERR_CAST(mnt_root);
+				goto out;
+			}
 
-	if (s->s_root) {
-		btrfs_close_devices(fs_devices);
-		free_fs_info(fs_info);
-		if ((flags ^ s->s_flags) & MS_RDONLY)
-			error = -EBUSY;
-	} else {
-		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
-		btrfs_sb(s)->bdev_holder = fs_type;
-		error = btrfs_fill_super(s, fs_devices, data);
-	}
-	if (error) {
-		deactivate_locked_super(s);
-		goto error_sec_opts;
+			down_write(&mnt_root->mnt_sb->s_umount);
+			error = btrfs_remount(mnt_root->mnt_sb, &flags, NULL);
+			up_write(&mnt_root->mnt_sb->s_umount);
+			if (error < 0) {
+				root = ERR_PTR(error);
+				mntput(mnt_root);
+				goto out;
+			}
+		}
 	}
-
-	fs_info = btrfs_sb(s);
-	error = setup_security_options(fs_info, s, &new_sec_opts);
-	if (error) {
-		deactivate_locked_super(s);
-		goto error_sec_opts;
+	if (IS_ERR(mnt_root)) {
+		root = ERR_CAST(mnt_root);
+		goto out;
 	}
 
-	return dget(s->s_root);
+	/* mount_subvol() will free subvol_name and mnt_root */
+	root = mount_subvol(subvol_name, subvol_objectid, flags,
+				    device_name, data, mnt_root);
 
-error_close_devices:
-	btrfs_close_devices(fs_devices);
-error_fs_info:
-	free_fs_info(fs_info);
-error_sec_opts:
-	security_free_mnt_opts(&new_sec_opts);
-	return ERR_PTR(error);
+out:
+	return root;
 }
 
 static void btrfs_resize_thread_pool(struct btrfs_fs_info *fs_info,
-- 
2.9.5

[PATCH 3/4] btrfs: split parse_early_options() in two

[Misono, Tomohiro]

Now parse_early_options() is used by both btrfs_mount() and mount_root().
However, the former only needs subvol related part and the latter needs
the others.

Therefore extract the subvol related parts from parse_early_options() and
move it to new parse function (parse_subvol_options()).

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
---
 fs/btrfs/super.c | 85 +++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 60 insertions(+), 25 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 1c34ca6..7edd74d 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -448,7 +448,8 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 		case Opt_subvolrootid:
 		case Opt_device:
 			/*
-			 * These are parsed by btrfs_parse_early_options
+			 * These are parsed by btrfs_parse_subvol_options
+			 * and btrfs_parse_early_options
 			 * and can be happily ignored here.
 			 */
 			break;
@@ -855,11 +856,63 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
  * only when we need to allocate a new super block.
  */
 static int btrfs_parse_early_options(const char *options, fmode_t flags,
-		void *holder, char **subvol_name, u64 *subvol_objectid,
-		struct btrfs_fs_devices **fs_devices)
+		void *holder, struct btrfs_fs_devices **fs_devices)
 {
 	substring_t args[MAX_OPT_ARGS];
 	char *device_name, *opts, *orig, *p;
+	int error = 0;
+
+	if (!options)
+		return 0;
+
+	/*
+	 * strsep changes the string, duplicate it because btrfs_parse_options
+	 * gets called later
+	 */
+	opts = kstrdup(options, GFP_KERNEL);
+	if (!opts)
+		return -ENOMEM;
+	orig = opts;
+
+	while ((p = strsep(&opts, ",")) != NULL) {
+		int token;
+		if (!*p)
+			continue;
+
+		token = match_token(p, tokens, args);
+		switch (token) {
+		case Opt_device:
+			device_name = match_strdup(&args[0]);
+			if (!device_name) {
+				error = -ENOMEM;
+				goto out;
+			}
+			error = btrfs_scan_one_device(device_name,
+					flags, holder, fs_devices);
+			kfree(device_name);
+			if (error)
+				goto out;
+			break;
+		default:
+			break;
+		}
+	}
+
+out:
+	kfree(orig);
+	return error;
+}
+
+/*
+ * Parse mount options that are related to subvolume id
+ *
+ * The value is later passed to mount_subvol()
+ */
+static int btrfs_parse_subvol_options(const char *options, fmode_t flags,
+		void *holder, char **subvol_name, u64 *subvol_objectid)
+{
+	substring_t args[MAX_OPT_ARGS];
+	char *opts, *orig, *p;
 	char *num = NULL;
 	int error = 0;
 
@@ -867,8 +920,8 @@ static int btrfs_parse_early_options(const char *options, fmode_t flags,
 		return 0;
 
 	/*
-	 * strsep changes the string, duplicate it because parse_options
-	 * gets called twice
+	 * strsep changes the string, duplicate it because
+	 * btrfs_parse_early_options gets called later
 	 */
 	opts = kstrdup(options, GFP_KERNEL);
 	if (!opts)
@@ -907,18 +960,6 @@ static int btrfs_parse_early_options(const char *options, fmode_t flags,
 		case Opt_subvolrootid:
 			pr_warn("BTRFS: 'subvolrootid' mount option is deprecated and has no effect\n");
 			break;
-		case Opt_device:
-			device_name = match_strdup(&args[0]);
-			if (!device_name) {
-				error = -ENOMEM;
-				goto out;
-			}
-			error = btrfs_scan_one_device(device_name,
-					flags, holder, fs_devices);
-			kfree(device_name);
-			if (error)
-				goto out;
-			break;
 		default:
 			break;
 		}
@@ -1492,18 +1533,14 @@ static struct dentry *mount_root(struct file_system_type *fs_type, int flags,
 	struct btrfs_fs_info *fs_info = NULL;
 	struct security_mnt_opts new_sec_opts;
 	fmode_t mode = FMODE_READ;
-	char *subvol_name = NULL;
-	u64 subvol_objectid = 0;
 	int error = 0;
 
 	if (!(flags & MS_RDONLY))
 		mode |= FMODE_WRITE;
 
 	error = btrfs_parse_early_options(data, mode, fs_type,
-					  &subvol_name, &subvol_objectid,
 					  &fs_devices);
 	if (error) {
-		kfree(subvol_name);
 		return ERR_PTR(error);
 	}
 
@@ -1614,7 +1651,6 @@ static struct dentry *mount_root(struct file_system_type *fs_type, int flags,
 static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 		const char *device_name, void *data)
 {
-	struct btrfs_fs_devices *fs_devices = NULL;
 	struct vfsmount *mnt_root;
 	struct dentry *root;
 	fmode_t mode = FMODE_READ;
@@ -1625,9 +1661,8 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 	if (!(flags & MS_RDONLY))
 		mode |= FMODE_WRITE;
 
-	error = btrfs_parse_early_options(data, mode, fs_type,
-					  &subvol_name, &subvol_objectid,
-					  &fs_devices);
+	error = btrfs_parse_subvol_options(data, mode, fs_type,
+					  &subvol_name, &subvol_objectid);
 	if (error) {
 		kfree(subvol_name);
 		return ERR_PTR(error);
-- 
2.9.5

Re: [PATCH 3/4] btrfs: split parse_early_options() in two

[David Sterba]

On Mon, Sep 25, 2017 at 04:28:36PM +0900, Misono, Tomohiro wrote:
> Now parse_early_options() is used by both btrfs_mount() and mount_root().
> However, the former only needs subvol related part and the latter needs
> the others.
> 
> Therefore extract the subvol related parts from parse_early_options() and
> move it to new parse function (parse_subvol_options()).
> 
> Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
> ---
>  fs/btrfs/super.c | 85 +++++++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 60 insertions(+), 25 deletions(-)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 1c34ca6..7edd74d 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -448,7 +448,8 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
>  		case Opt_subvolrootid:
>  		case Opt_device:
>  			/*
> -			 * These are parsed by btrfs_parse_early_options
> +			 * These are parsed by btrfs_parse_subvol_options
> +			 * and btrfs_parse_early_options
>  			 * and can be happily ignored here.
>  			 */
>  			break;
> @@ -855,11 +856,63 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
>   * only when we need to allocate a new super block.
>   */
>  static int btrfs_parse_early_options(const char *options, fmode_t flags,
> -		void *holder, char **subvol_name, u64 *subvol_objectid,
> -		struct btrfs_fs_devices **fs_devices)
> +		void *holder, struct btrfs_fs_devices **fs_devices)
>  {
>  	substring_t args[MAX_OPT_ARGS];
>  	char *device_name, *opts, *orig, *p;
> +	int error = 0;
> +
> +	if (!options)
> +		return 0;
> +
> +	/*
> +	 * strsep changes the string, duplicate it because btrfs_parse_options
> +	 * gets called later
> +	 */
> +	opts = kstrdup(options, GFP_KERNEL);
> +	if (!opts)
> +		return -ENOMEM;
> +	orig = opts;
> +
> +	while ((p = strsep(&opts, ",")) != NULL) {
> +		int token;
> +		if (!*p)
> +			continue;
> +
> +		token = match_token(p, tokens, args);
> +		switch (token) {
> +		case Opt_device:

Please rewrite this as a simple 'if'.

> +			device_name = match_strdup(&args[0]);
> +			if (!device_name) {
> +				error = -ENOMEM;
> +				goto out;
> +			}
> +			error = btrfs_scan_one_device(device_name,
> +					flags, holder, fs_devices);
> +			kfree(device_name);
> +			if (error)
> +				goto out;
> +			break;
> +		default:
> +			break;
> +		}
> +	}
> +
> +out:
> +	kfree(orig);
> +	return error;
> +}
> +
> +/*
> + * Parse mount options that are related to subvolume id
> + *
> + * The value is later passed to mount_subvol()
> + */
> +static int btrfs_parse_subvol_options(const char *options, fmode_t flags,
> +		void *holder, char **subvol_name, u64 *subvol_objectid)
> +{
> +	substring_t args[MAX_OPT_ARGS];
> +	char *opts, *orig, *p;
>  	char *num = NULL;
>  	int error = 0;
>  
> @@ -867,8 +920,8 @@ static int btrfs_parse_early_options(const char *options, fmode_t flags,
>  		return 0;
>  
>  	/*
> -	 * strsep changes the string, duplicate it because parse_options
> -	 * gets called twice
> +	 * strsep changes the string, duplicate it because
> +	 * btrfs_parse_early_options gets called later
>  	 */
>  	opts = kstrdup(options, GFP_KERNEL);
>  	if (!opts)
> @@ -907,18 +960,6 @@ static int btrfs_parse_early_options(const char *options, fmode_t flags,
>  		case Opt_subvolrootid:
>  			pr_warn("BTRFS: 'subvolrootid' mount option is deprecated and has no effect\n");
>  			break;
> -		case Opt_device:
> -			device_name = match_strdup(&args[0]);
> -			if (!device_name) {
> -				error = -ENOMEM;
> -				goto out;
> -			}
> -			error = btrfs_scan_one_device(device_name,
> -					flags, holder, fs_devices);
> -			kfree(device_name);
> -			if (error)
> -				goto out;
> -			break;
>  		default:
>  			break;
>  		}
> @@ -1492,18 +1533,14 @@ static struct dentry *mount_root(struct file_system_type *fs_type, int flags,
>  	struct btrfs_fs_info *fs_info = NULL;
>  	struct security_mnt_opts new_sec_opts;
>  	fmode_t mode = FMODE_READ;
> -	char *subvol_name = NULL;
> -	u64 subvol_objectid = 0;
>  	int error = 0;
>  
>  	if (!(flags & MS_RDONLY))
>  		mode |= FMODE_WRITE;
>  
>  	error = btrfs_parse_early_options(data, mode, fs_type,
> -					  &subvol_name, &subvol_objectid,
>  					  &fs_devices);
>  	if (error) {
> -		kfree(subvol_name);
>  		return ERR_PTR(error);
>  	}
>  
> @@ -1614,7 +1651,6 @@ static struct dentry *mount_root(struct file_system_type *fs_type, int flags,
>  static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
>  		const char *device_name, void *data)
>  {
> -	struct btrfs_fs_devices *fs_devices = NULL;
>  	struct vfsmount *mnt_root;
>  	struct dentry *root;
>  	fmode_t mode = FMODE_READ;
> @@ -1625,9 +1661,8 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
>  	if (!(flags & MS_RDONLY))
>  		mode |= FMODE_WRITE;
>  
> -	error = btrfs_parse_early_options(data, mode, fs_type,
> -					  &subvol_name, &subvol_objectid,
> -					  &fs_devices);
> +	error = btrfs_parse_subvol_options(data, mode, fs_type,
> +					  &subvol_name, &subvol_objectid);
>  	if (error) {
>  		kfree(subvol_name);
>  		return ERR_PTR(error);
> -- 
> 2.9.5
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

[PATCH 4/4] btrfs: remove unused setup_root_args()

[Misono, Tomohiro]

Since setup_root_args() is not used anymore, just remove it.

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
---
 fs/btrfs/super.c | 35 -----------------------------------
 1 file changed, 35 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 7edd74d..f589c5b 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1367,41 +1367,6 @@ static inline int is_subvolume_inode(struct inode *inode)
 	return 0;
 }
 
-/*
- * 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)
-{
-	char *buf, *dst, *sep;
-
-	if (!args)
-		return kstrdup("subvolid=0", 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;
-
-	while (1) {
-		sep = strchrnul(args, ',');
-		if (!strstarts(args, "subvol=") &&
-		    !strstarts(args, "subvolid=")) {
-			memcpy(dst, args, sep - args);
-			dst += sep - args;
-			*dst++ = ',';
-		}
-		if (*sep)
-			args = sep + 1;
-		else
-			break;
-	}
-	strcpy(dst, "subvolid=0");
-
-	return buf;
-}
-
 static struct dentry *mount_subvol(const char *subvol_name, u64 subvol_objectid,
 				   int flags, const char *device_name,
 				   char *data, struct vfsmount *mnt)
-- 
2.9.5

Re: [PATCH v3 0/4] btrfs: cleanup mount path

[David Sterba]

On Mon, Sep 25, 2017 at 04:26:30PM +0900, Misono, Tomohiro wrote:
> Summary:
> Cleanup mount path by avoiding calling btrfs_mount() twice.
> No functional change. See below for longer explanation.
> 
> Changelog:
> v3:
>   Reorganized patches again into four and added comments to the source.
>   Each patch can be applied and compiled while maintaining functionality.
>   The first one is the preparation and the second one is the main part.
>   The last two are small cleanups.

I'm conditionally adding this series to for-next for testing.

Re: [PATCH v3 0/4] btrfs: cleanup mount path

[David Sterba]

On Mon, Oct 16, 2017 at 05:15:38PM +0200, David Sterba wrote:
> On Mon, Sep 25, 2017 at 04:26:30PM +0900, Misono, Tomohiro wrote:
> > Summary:
> > Cleanup mount path by avoiding calling btrfs_mount() twice.
> > No functional change. See below for longer explanation.
> > 
> > Changelog:
> > v3:
> >   Reorganized patches again into four and added comments to the source.
> >   Each patch can be applied and compiled while maintaining functionality.
> >   The first one is the preparation and the second one is the main part.
> >   The last two are small cleanups.
> 
> I'm conditionally adding this series to for-next for testing.

No problems while this patch has been in for-next, so I'm going to add
that to 4.16 queue. Please update the patchset according to my comments.
Also please review if there's anything relevant for th MS_* and SB_*
rename that happened in 4.15 (1751e8a6cb935). Thanks.