Hi,
在 2024/03/25 20:04, Christian Brauner 写道:
On Mon, Mar 25, 2024 at 07:51:27PM +0800, Yu Kuai wrote:
Hi,
在 2024/03/24 0:11, Christian Brauner 写道:
Last kernel release we introduce CONFIG_BLK_DEV_WRITE_MOUNTED. By
default this option is set. When it is set the long-standing behavior
of being able to write to mounted block devices is enabled.
But in order to guard against unintended corruption by writing to the
block device buffer cache CONFIG_BLK_DEV_WRITE_MOUNTED can be turned
off. In that case it isn't possible to write to mounted block devices
anymore.
A filesystem may open its block devices with BLK_OPEN_RESTRICT_WRITES
which disallows concurrent BLK_OPEN_WRITE access. When we still had the
bdev handle around we could recognize BLK_OPEN_RESTRICT_WRITES because
the mode was passed around. Since we managed to get rid of the bdev
handle we changed that logic to recognize BLK_OPEN_RESTRICT_WRITES based
on whether the file was opened writable and writes to that block device
are blocked. That logic doesn't work because we do allow
BLK_OPEN_RESTRICT_WRITES to be specified without BLK_OPEN_WRITE.
I don't get it here, looks like there are no such use case. All users
passed in BLK_OPEN_RESTRICT_WRITES together with BLK_OPEN_WRITE.
sb_open_mode() does
#define sb_open_mode(flags) \
(BLK_OPEN_READ | BLK_OPEN_RESTRICT_WRITES | \
(((flags) & SB_RDONLY) ? 0 : BLK_OPEN_WRITE))
Yes, you're right, thanks for the notice. And the problem that I
described should also exist.
BTW, do you agree that using O_EXCL is not correct here?
Thanks,
Kuai
.
