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

["Darrick J. Wong" <djwong@kernel.org>]

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?

--D

> Thanks,
> 
> Bart.