Re: [PATCH V2] Documentation: Document the kernel flag bdev_allow_write_mounted

["Guilherme G. Piccoli" <gpiccoli@igalia.com>]

On 23/08/2024 14:05, Darrick J. Wong wrote:
> On Fri, Aug 23, 2024 at 09:11:22AM -0700, Bart Van Assche wrote:
>> On 8/23/24 7:26 AM, Guilherme G. Piccoli wrote:
>>> +	bdev_allow_write_mounted=
>>> +			Format: <bool>
>>> +			Control the ability of directly writing to mounted block
>>> +			devices' page cache, i.e., allow / disallow writes that
>>> +			bypasses the FS. This was implemented as a means to
>>> +			prevent fuzzers from crashing the kernel by overwriting
>>> +			the metadata underneath a mounted FS without its awareness.
>>> +			This also prevents destructive formatting of mounted
>>> +			filesystems by naive storage tooling that don't use
>>> +			O_EXCL. Default is Y and can be changed through the
>>> +			Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED.
>>> +
>>
>> Does this flag also affect direct I/O? If so, does this mean that the
>> reference to the page cache should be left out?
> 
> I think it does affect directio, since the validation is done at open
> time via bdev_may_open, right?
> 

Indeed, good point! It does affect direct I/O, I've just tested in
6.11-rc3 using dd (with and w/o oflags=direct), same result.

I'll resend, dropping the mention to page cache - thanks!

Guilherme