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Subject[PATCH 1/2] vfs: Provide function to get superblock and wait for it to thaw
Date
In quota code we need to find a superblock corresponding to a device and wait
for superblock to be unfrozen. However this waiting has to happen without
s_umount semaphore because that is required for superblock to thaw. So provide
a function in VFS for this to keep dances with s_umount where they belong.

Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/super.c | 50 ++++++++++++++++++++++++++++++++++++++------------
include/linux/fs.h | 1 +
2 files changed, 39 insertions(+), 12 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 6015c02..1f657d6 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -593,15 +593,8 @@ void iterate_supers_type(struct file_system_type *type,

EXPORT_SYMBOL(iterate_supers_type);

-/**
- * get_super - get the superblock of a device
- * @bdev: device to get the superblock for
- *
- * Scans the superblock list and finds the superblock of the file system
- * mounted on the device given. %NULL is returned if no match is found.
- */
-
-struct super_block *get_super(struct block_device *bdev)
+static struct super_block *__get_super(struct block_device *bdev,
+ bool wait_thaw)
{
struct super_block *sb;

@@ -618,9 +611,13 @@ rescan:
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
/* still alive? */
- if (sb->s_root && (sb->s_flags & MS_BORN))
- return sb;
- up_read(&sb->s_umount);
+ if (sb->s_root && (sb->s_flags & MS_BORN)) {
+ if (!wait_thaw || sb->s_frozen == SB_UNFROZEN)
+ return sb;
+ up_read(&sb->s_umount);
+ vfs_check_frozen(sb, SB_FREEZE_WRITE);
+ } else
+ up_read(&sb->s_umount);
/* nope, got unmounted */
spin_lock(&sb_lock);
__put_super(sb);
@@ -631,9 +628,38 @@ rescan:
return NULL;
}

+/**
+ * get_super - get the superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device given. %NULL is returned if no match is found.
+ * Note that the returned superblock may be frozen.
+ */
+
+struct super_block *get_super(struct block_device *bdev)
+{
+ return __get_super(bdev, false);
+}
EXPORT_SYMBOL(get_super);

/**
+ * get_super_thawed - get thawed superblock of a device
+ * @bdev: device to get the superblock for
+ *
+ * Scans the superblock list and finds the superblock of the file system
+ * mounted on the device. The superblock is returned once it is thawed
+ * (or immediately if it was not frozen). %NULL is returned if no match
+ * is found.
+ */
+
+struct super_block *get_super_thawed(struct block_device *bdev)
+{
+ return __get_super(bdev, true);
+}
+EXPORT_SYMBOL(get_super_thawed);
+
+/**
* get_active_super - get an active reference to the superblock of a device
* @bdev: device to get the superblock for
*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 386da09..69cd5bb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2496,6 +2496,7 @@ extern void get_filesystem(struct file_system_type *fs);
extern void put_filesystem(struct file_system_type *fs);
extern struct file_system_type *get_fs_type(const char *name);
extern struct super_block *get_super(struct block_device *);
+extern struct super_block *get_super_thawed(struct block_device *);
extern struct super_block *get_active_super(struct block_device *bdev);
extern void drop_super(struct super_block *sb);
extern void iterate_supers(void (*)(struct super_block *, void *), void *);
--
1.7.1


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