fs: Provide function to get superblock with exclusive s_umount

Quota code will need a variant of get_super_thawed() that returns
superblock with s_umount held in exclusive mode to serialize quota on
and quota off operations. Provide this functionality.

Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/super.c b/fs/super.c
index c183835..f7f7242 100644 (file)
--- a/fs/super.c
+++ b/fs/super.c
@@ -558,6 +558,13 @@ void drop_super(struct super_block *sb)
 
 EXPORT_SYMBOL(drop_super);
 
+void drop_super_exclusive(struct super_block *sb)
+{
+       up_write(&sb->s_umount);
+       put_super(sb);
+}
+EXPORT_SYMBOL(drop_super_exclusive);
+
 /**
  *     iterate_supers - call function for all active superblocks
  *     @f: function to call
@@ -628,15 +635,7 @@ 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 excl)
 {
        struct super_block *sb;
 
@@ -651,11 +650,17 @@ rescan:
                if (sb->s_bdev == bdev) {
                        sb->s_count++;
                        spin_unlock(&sb_lock);
-                       down_read(&sb->s_umount);
+                       if (!excl)
+                               down_read(&sb->s_umount);
+                       else
+                               down_write(&sb->s_umount);
                        /* still alive? */
                        if (sb->s_root && (sb->s_flags & MS_BORN))
                                return sb;
-                       up_read(&sb->s_umount);
+                       if (!excl)
+                               up_read(&sb->s_umount);
+                       else
+                               up_write(&sb->s_umount);
                        /* nope, got unmounted */
                        spin_lock(&sb_lock);
                        __put_super(sb);
@@ -666,32 +671,67 @@ rescan:
        return NULL;
 }
 
-EXPORT_SYMBOL(get_super);
-
 /**
- *     get_super_thawed - get thawed superblock of a device
+ *     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. The superblock is returned once it is thawed
- *     (or immediately if it was not frozen). %NULL is returned if no match
- *     is found.
+ *     mounted on the device given. %NULL is returned if no match is found.
  */
-struct super_block *get_super_thawed(struct block_device *bdev)
+struct super_block *get_super(struct block_device *bdev)
+{
+       return __get_super(bdev, false);
+}
+EXPORT_SYMBOL(get_super);
+
+static struct super_block *__get_super_thawed(struct block_device *bdev,
+                                             bool excl)
 {
        while (1) {
-               struct super_block *s = get_super(bdev);
+               struct super_block *s = __get_super(bdev, excl);
                if (!s || s->s_writers.frozen == SB_UNFROZEN)
                        return s;
-               up_read(&s->s_umount);
+               if (!excl)
+                       up_read(&s->s_umount);
+               else
+                       up_write(&s->s_umount);
                wait_event(s->s_writers.wait_unfrozen,
                           s->s_writers.frozen == SB_UNFROZEN);
                put_super(s);
        }
 }
+
+/**
+ *     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_thawed(bdev, false);
+}
 EXPORT_SYMBOL(get_super_thawed);
 
 /**
+ *     get_super_exclusive_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) and s_umount semaphore is held
+ *     in exclusive mode. %NULL is returned if no match is found.
+ */
+struct super_block *get_super_exclusive_thawed(struct block_device *bdev)
+{
+       return __get_super_thawed(bdev, true);
+}
+EXPORT_SYMBOL(get_super_exclusive_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 dc0478c..d04cfde 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2949,8 +2949,10 @@ 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_super_exclusive_thawed(struct block_device *bdev);
 extern struct super_block *get_active_super(struct block_device *bdev);
 extern void drop_super(struct super_block *sb);
+extern void drop_super_exclusive(struct super_block *sb);
 extern void iterate_supers(void (*)(struct super_block *, void *), void *);
 extern void iterate_supers_type(struct file_system_type *,
                                void (*)(struct super_block *, void *), void *);