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nbd: do not allow two clients at the same time 

Two nbd-clients at same time are bad idea, and cause WARN_ON from nbd in
2.6.28-rc7 from sysfs_add_one.  This simply prevents that from happening.

To reproduce:

 cat /dev/zero | head -c 10000000 > /tmp/delme.fstest.fs
 nbd-server 9100 -l /anyone.can.connect > /tmp/delme.fstest.fs &
 sleep 1
 nbd-client localhost 9100 /dev/nd0 &
 nbd-client localhost 9100 /dev/nd0 &

Signed-off-by: Pavel Machek <pavel@suse.cz>
Acked-by: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Pavel Machek 2009-01-15 13:51:03 -08:00 committed by Linus Torvalds
parent 1bcbf31337
commit c91192d66d
1 changed files with 4 additions and 0 deletions
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4
drivers/block/nbd.c
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@ -406,6 +406,7 @@ static int nbd_do_it(struct nbd_device *lo)
ret = sysfs_create_file(&disk_to_dev(lo->disk)->kobj, &pid_attr.attr);
if (ret) {
printk(KERN_ERR "nbd: sysfs_create_file failed!");
lo->pid = 0;
return ret;
}
@ -413,6 +414,7 @@ static int nbd_do_it(struct nbd_device *lo)
nbd_end_request(req);
sysfs_remove_file(&disk_to_dev(lo->disk)->kobj, &pid_attr.attr);
lo->pid = 0;
return 0;
}
@ -648,6 +650,8 @@ static int nbd_ioctl(struct block_device *bdev, fmode_t mode,
set_capacity(lo->disk, lo->bytesize >> 9);
return 0;
case NBD_DO_IT:
if (lo->pid)
return -EBUSY;
if (!lo->file)
return -EINVAL;
thread = kthread_create(nbd_thread, lo, lo->disk->disk_name);