linux-kernel - Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

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Date:   Mon, 2 Oct 2023 19:57:03 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     John Garry <john.g.garry@...cle.com>,
        Bart Van Assche <bvanassche@....org>,
        Eric Biggers <ebiggers@...nel.org>, axboe@...nel.dk,
        kbusch@...nel.org, hch@....de, sagi@...mberg.me,
        jejb@...ux.ibm.com, martin.petersen@...cle.com,
        viro@...iv.linux.org.uk, brauner@...nel.org,
        chandan.babu@...cle.com, dchinner@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-api@...r.kernel.org,
        Prasad Singamsetty <prasad.singamsetty@...cle.com>
Subject: Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

On Tue, Oct 03, 2023 at 12:51:49PM +1100, Dave Chinner wrote:
> On Mon, Oct 02, 2023 at 10:51:36AM +0100, John Garry wrote:
> > On 01/10/2023 14:23, Bart Van Assche wrote:
> > > On 9/29/23 15:49, Eric Biggers wrote:
> > > > On Fri, Sep 29, 2023 at 10:27:08AM +0000, John Garry wrote:
> > > > > diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h
> > > > > index 7cab2c65d3d7..c99d7cac2aa6 100644
> > > > > --- a/include/uapi/linux/stat.h
> > > > > +++ b/include/uapi/linux/stat.h
> > > > > @@ -127,7 +127,10 @@ struct statx {
> > > > >       __u32    stx_dio_mem_align;    /* Memory buffer alignment
> > > > > for direct I/O */
> > > > >       __u32    stx_dio_offset_align;    /* File offset alignment
> > > > > for direct I/O */
> > > > >       /* 0xa0 */
> > > > > -    __u64    __spare3[12];    /* Spare space for future expansion */
> > > > > +    __u32    stx_atomic_write_unit_max;
> > > > > +    __u32    stx_atomic_write_unit_min;
> > > > 
> > > > Maybe min first and then max?  That seems a bit more natural, and a
> > > > lot of the
> > > > code you've written handle them in that order.
> > 
> > ok, I think it's fine to reorder
> > 
> > > > 
> > > > > +#define STATX_ATTR_WRITE_ATOMIC        0x00400000 /* File
> > > > > supports atomic write operations */
> > > > 
> > > > How would this differ from stx_atomic_write_unit_min != 0?
> > 
> > Yeah, I suppose that we can just not set this for the case of
> > stx_atomic_write_unit_min == 0.
> 
> Please use the STATX_ATTR_WRITE_ATOMIC flag to indicate that the
> filesystem, file and underlying device support atomic writes when
> the values are non-zero. The whole point of the attribute mask is
> that the caller can check the mask for supported functionality
> without having to read every field in the statx structure to
> determine if the functionality it wants is present.

^^ Seconding what Dave said.

--D

> -Dave.
> -- 
> Dave Chinner
> david@...morbit.com