block: make blkdev_get/put() handle exclusive access
Over time, block layer has accumulated a set of APIs dealing with bdev
open, close, claim and release.
* blkdev_get/put() are the primary open and close functions.
* bd_claim/release() deal with exclusive open.
* open/close_bdev_exclusive() are combination of open and claim and
the other way around, respectively.
* bd_link/unlink_disk_holder() to create and remove holder/slave
symlinks.
* open_by_devnum() wraps bdget() + blkdev_get().
The interface is a bit confusing and the decoupling of open and claim
makes it impossible to properly guarantee exclusive access as
in-kernel open + claim sequence can disturb the existing exclusive
open even before the block layer knows the current open if for another
exclusive access. Reorganize the interface such that,
* blkdev_get() is extended to include exclusive access management.
@holder argument is added and, if is @FMODE_EXCL specified, it will
gain exclusive access atomically w.r.t. other exclusive accesses.
* blkdev_put() is similarly extended. It now takes @mode argument and
if @FMODE_EXCL is set, it releases an exclusive access. Also, when
the last exclusive claim is released, the holder/slave symlinks are
removed automatically.
* bd_claim/release() and close_bdev_exclusive() are no longer
necessary and either made static or removed.
* bd_link_disk_holder() remains the same but bd_unlink_disk_holder()
is no longer necessary and removed.
* open_bdev_exclusive() becomes a simple wrapper around lookup_bdev()
and blkdev_get(). It also has an unexpected extra bdev_read_only()
test which probably should be moved into blkdev_get().
* open_by_devnum() is modified to take @holder argument and pass it to
blkdev_get().
Most of bdev open/close operations are unified into blkdev_get/put()
and most exclusive accesses are tested atomically at the open time (as
it should). This cleans up code and removes some, both valid and
invalid, but unnecessary all the same, corner cases.
open_bdev_exclusive() and open_by_devnum() can use further cleanup -
rename to blkdev_get_by_path() and blkdev_get_by_devt() and drop
special features. Well, let's leave them for another day.
Most conversions are straight-forward. drbd conversion is a bit more
involved as there was some reordering, but the logic should stay the
same.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Neil Brown <neilb@suse.de>
Acked-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Philipp Reisner <philipp.reisner@linbit.com>
Cc: Peter Osterlund <petero2@telia.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <joel.becker@oracle.com>
Cc: Alex Elder <aelder@sgi.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: dm-devel@redhat.com
Cc: drbd-dev@lists.linbit.com
Cc: Leo Chen <leochen@broadcom.com>
Cc: Scott Branden <sbranden@broadcom.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Cc: Joern Engel <joern@logfs.org>
Cc: reiserfs-devel@vger.kernel.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 9329068..fc48912 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -660,7 +660,7 @@
else if (bdev->bd_contains == bdev)
return true; /* is a whole device which isn't held */
- else if (whole->bd_holder == bd_claim)
+ else if (whole->bd_holder == bd_may_claim)
return true; /* is a partition of a device that is being partitioned */
else if (whole->bd_holder != NULL)
return false; /* is a partition of a held device */
@@ -807,10 +807,10 @@
{
/* note that for a whole device bd_holders
* will be incremented twice, and bd_holder will
- * be set to bd_claim before being set to holder
+ * be set to bd_may_claim before being set to holder
*/
whole->bd_holders++;
- whole->bd_holder = bd_claim;
+ whole->bd_holder = bd_may_claim;
bdev->bd_holders++;
bdev->bd_holder = holder;
}
@@ -835,37 +835,7 @@
__bd_abort_claiming(whole, holder); /* not actually an abort */
}
-/**
- * bd_claim - claim a block device
- * @bdev: block device to claim
- * @holder: holder trying to claim @bdev
- *
- * Try to claim @bdev which must have been opened successfully.
- *
- * CONTEXT:
- * Might sleep.
- *
- * RETURNS:
- * 0 if successful, -EBUSY if @bdev is already claimed.
- */
-int bd_claim(struct block_device *bdev, void *holder)
-{
- struct block_device *whole = bdev->bd_contains;
- int res;
-
- might_sleep();
-
- spin_lock(&bdev_lock);
- res = bd_prepare_to_claim(bdev, whole, holder);
- if (res == 0)
- __bd_claim(bdev, whole, holder);
- spin_unlock(&bdev_lock);
-
- return res;
-}
-EXPORT_SYMBOL(bd_claim);
-
-void bd_release(struct block_device *bdev)
+static void bd_release(struct block_device *bdev)
{
spin_lock(&bdev_lock);
if (!--bdev->bd_contains->bd_holders)
@@ -875,8 +845,6 @@
spin_unlock(&bdev_lock);
}
-EXPORT_SYMBOL(bd_release);
-
#ifdef CONFIG_SYSFS
static int add_symlink(struct kobject *from, struct kobject *to)
{
@@ -943,7 +911,7 @@
}
EXPORT_SYMBOL_GPL(bd_link_disk_holder);
-void bd_unlink_disk_holder(struct block_device *bdev)
+static void bd_unlink_disk_holder(struct block_device *bdev)
{
struct gendisk *disk = bdev->bd_holder_disk;
@@ -954,7 +922,9 @@
del_symlink(disk->slave_dir, &part_to_dev(bdev->bd_part)->kobj);
del_symlink(bdev->bd_part->holder_dir, &disk_to_dev(disk)->kobj);
}
-EXPORT_SYMBOL_GPL(bd_unlink_disk_holder);
+#else
+static inline void bd_unlink_disk_holder(struct block_device *bdev)
+{ }
#endif
/*
@@ -964,12 +934,12 @@
* to be used for internal purposes. If you ever need it - reconsider
* your API.
*/
-struct block_device *open_by_devnum(dev_t dev, fmode_t mode)
+struct block_device *open_by_devnum(dev_t dev, fmode_t mode, void *holder)
{
struct block_device *bdev = bdget(dev);
int err = -ENOMEM;
if (bdev)
- err = blkdev_get(bdev, mode);
+ err = blkdev_get(bdev, mode, holder);
return err ? ERR_PTR(err) : bdev;
}
@@ -1235,17 +1205,37 @@
return ret;
}
-int blkdev_get(struct block_device *bdev, fmode_t mode)
+int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
{
- return __blkdev_get(bdev, mode, 0);
+ struct block_device *whole = NULL;
+ int res;
+
+ WARN_ON_ONCE((mode & FMODE_EXCL) && !holder);
+
+ if ((mode & FMODE_EXCL) && holder) {
+ whole = bd_start_claiming(bdev, holder);
+ if (IS_ERR(whole)) {
+ bdput(bdev);
+ return PTR_ERR(whole);
+ }
+ }
+
+ res = __blkdev_get(bdev, mode, 0);
+
+ if (whole) {
+ if (res == 0)
+ bd_finish_claiming(bdev, whole, holder);
+ else
+ bd_abort_claiming(whole, holder);
+ }
+
+ return res;
}
EXPORT_SYMBOL(blkdev_get);
static int blkdev_open(struct inode * inode, struct file * filp)
{
- struct block_device *whole = NULL;
struct block_device *bdev;
- int res;
/*
* Preserve backwards compatibility and allow large file access
@@ -1266,26 +1256,9 @@
if (bdev == NULL)
return -ENOMEM;
- if (filp->f_mode & FMODE_EXCL) {
- whole = bd_start_claiming(bdev, filp);
- if (IS_ERR(whole)) {
- bdput(bdev);
- return PTR_ERR(whole);
- }
- }
-
filp->f_mapping = bdev->bd_inode->i_mapping;
- res = blkdev_get(bdev, filp->f_mode);
-
- if (whole) {
- if (res == 0)
- bd_finish_claiming(bdev, whole, filp);
- else
- bd_abort_claiming(whole, filp);
- }
-
- return res;
+ return blkdev_get(bdev, filp->f_mode, filp);
}
static int __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
@@ -1329,6 +1302,13 @@
int blkdev_put(struct block_device *bdev, fmode_t mode)
{
+ if (mode & FMODE_EXCL) {
+ mutex_lock(&bdev->bd_mutex);
+ bd_release(bdev);
+ if (!bdev->bd_holders)
+ bd_unlink_disk_holder(bdev);
+ mutex_unlock(&bdev->bd_mutex);
+ }
return __blkdev_put(bdev, mode, 0);
}
EXPORT_SYMBOL(blkdev_put);
@@ -1336,8 +1316,7 @@
static int blkdev_close(struct inode * inode, struct file * filp)
{
struct block_device *bdev = I_BDEV(filp->f_mapping->host);
- if (bdev->bd_holder == filp)
- bd_release(bdev);
+
return blkdev_put(bdev, filp->f_mode);
}
@@ -1494,55 +1473,27 @@
*/
struct block_device *open_bdev_exclusive(const char *path, fmode_t mode, void *holder)
{
- struct block_device *bdev, *whole;
+ struct block_device *bdev;
int error;
bdev = lookup_bdev(path);
if (IS_ERR(bdev))
return bdev;
- whole = bd_start_claiming(bdev, holder);
- if (IS_ERR(whole)) {
- bdput(bdev);
- return whole;
+ error = blkdev_get(bdev, mode | FMODE_EXCL, holder);
+ if (error)
+ return ERR_PTR(error);
+
+ if ((mode & FMODE_WRITE) && bdev_read_only(bdev)) {
+ blkdev_put(bdev, mode);
+ return ERR_PTR(-EACCES);
}
- error = blkdev_get(bdev, mode);
- if (error)
- goto out_abort_claiming;
-
- error = -EACCES;
- if ((mode & FMODE_WRITE) && bdev_read_only(bdev))
- goto out_blkdev_put;
-
- bd_finish_claiming(bdev, whole, holder);
return bdev;
-
-out_blkdev_put:
- blkdev_put(bdev, mode);
-out_abort_claiming:
- bd_abort_claiming(whole, holder);
- return ERR_PTR(error);
}
EXPORT_SYMBOL(open_bdev_exclusive);
-/**
- * close_bdev_exclusive - close a blockdevice opened by open_bdev_exclusive()
- *
- * @bdev: blockdevice to close
- * @mode: mode, must match that used to open.
- *
- * This is the counterpart to open_bdev_exclusive().
- */
-void close_bdev_exclusive(struct block_device *bdev, fmode_t mode)
-{
- bd_release(bdev);
- blkdev_put(bdev, mode);
-}
-
-EXPORT_SYMBOL(close_bdev_exclusive);
-
int __invalidate_device(struct block_device *bdev)
{
struct super_block *sb = get_super(bdev);