Il 23/04/2014 05:42, Qiang Huang ha scritto:
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
commit 3a2d63f87989e01437ba994df5f297528c353d7d upstream.
There are two problems with shutdown in the NBD driver.
1: Receiving the NBD_DISCONNECT ioctl does not sync the filesystem.
This patch adds the sync operation into __nbd_ioctl()'s
NBD_DISCONNECT handler. This is useful because BLKFLSBUF is restricted
to processes that have CAP_SYS_ADMIN, and the NBD client may not
possess it (fsync of the block device does not sync the filesystem,
either).
2: Once we clear the socket we have no guarantee that later reads will
come from the same backing storage.
The patch adds calls to kill_bdev() in __nbd_ioctl()'s socket
clearing code so the page cache is cleaned, lest reads that hit on the
page cache will return stale data from the previously-accessible disk.
Example:
# qemu-nbd -r -c/dev/nbd0 /dev/sr0
# file -s /dev/nbd0
/dev/stdin: # UDF filesystem data (version 1.5) etc.
# qemu-nbd -d /dev/nbd0
# qemu-nbd -r -c/dev/nbd0 /dev/sda
# file -s /dev/nbd0
/dev/stdin: # UDF filesystem data (version 1.5) etc.
While /dev/sda has:
# file -s /dev/sda
/dev/sda: x86 boot sector; etc.
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Acked-by: Paul Clements <Paul.Clements@xxxxxxxxxxxx>
Cc: Alex Bligh <alex@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.2:
- Adjusted context
- s/\bnbd\b/lo/
- Incorporate export of kill_bdev() from commit ff01bb483265
('fs: move code out of buffer.c')]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
[hq: Backported to 3.4: Adjusted context]
Signed-off-by: Qiang Huang <h.huangqiang@xxxxxxxxxx>
---
drivers/block/nbd.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index d724da5..35fc569 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -584,10 +584,17 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
struct request sreq;
dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
+ if (!nbd->sock)
+ return -EINVAL;
+ mutex_unlock(&nbd->tx_lock);
+ fsync_bdev(bdev);
+ mutex_lock(&nbd->tx_lock);
blk_rq_init(NULL, &sreq);
sreq.cmd_type = REQ_TYPE_SPECIAL;
nbd_cmd(&sreq) = NBD_CMD_DISC;
+
+ /* Check again after getting mutex back. */
if (!nbd->sock)
return -EINVAL;
@@ -606,6 +613,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
nbd_clear_que(nbd);
BUG_ON(!list_empty(&nbd->queue_head));
BUG_ON(!list_empty(&nbd->waiting_queue));
+ kill_bdev(bdev);
if (file)
fput(file);
return 0;
@@ -688,6 +696,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
nbd->file = NULL;
nbd_clear_que(nbd);
dev_warn(disk_to_dev(nbd->disk), "queue cleared\n");
+ kill_bdev(bdev);
if (file)
fput(file);
nbd->bytesize = 0;
-- 1.8.3
Backport looks good, and a good idea too.
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Paolo
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