Re: [PATCH v2 2/3] xfs_io: Add RWF_DONTCACHE support to pwritev2

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

On Wed, Mar 05, 2025 at 03:57:47PM +0530, Ritesh Harjani (IBM) wrote:
> Add per-io RWF_DONTCACHE support flag to pwritev2().
> This enables xfs_io to perform uncached buffered-io writes.
> 
> e.g. xfs_io -fc "pwrite -U -V 1 0 16K" /mnt/f1
> 
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> ---
>  include/linux.h   |  5 +++++
>  io/pwrite.c       | 14 ++++++++++++--
>  man/man8/xfs_io.8 |  8 +++++++-
>  3 files changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux.h b/include/linux.h
> index b3516d54..6e83e073 100644
> --- a/include/linux.h
> +++ b/include/linux.h
> @@ -237,6 +237,11 @@ struct fsxattr {
>  #define RWF_ATOMIC	((__kernel_rwf_t)0x00000040)
>  #endif
>  
> +/* buffered IO that drops the cache after reading or writing data */
> +#ifndef RWF_DONTCACHE
> +#define RWF_DONTCACHE	((__kernel_rwf_t)0x00000080)
> +#endif
> +
>  /*
>   * Reminder: anything added to this file will be compiled into downstream
>   * userspace projects!
> diff --git a/io/pwrite.c b/io/pwrite.c
> index fab59be4..5fb0253f 100644
> --- a/io/pwrite.c
> +++ b/io/pwrite.c
> @@ -45,6 +45,7 @@ pwrite_help(void)
>  " -N   -- Perform the pwritev2() with RWF_NOWAIT\n"
>  " -D   -- Perform the pwritev2() with RWF_DSYNC\n"
>  " -A   -- Perform the pwritev2() with RWF_ATOMIC\n"
> +" -U   -- Perform the pwritev2() with Uncached/RWF_DONTCACHE\n"

I would have just said "...with RWF_DONTCACHE" because that's a lot more
precise.

With that shortened, this looks pretty straightforward.
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

>  #endif
>  "\n"));
>  }
> @@ -285,7 +286,7 @@ pwrite_f(
>  	init_cvtnum(&fsblocksize, &fssectsize);
>  	bsize = fsblocksize;
>  
> -	while ((c = getopt(argc, argv, "Ab:BCdDf:Fi:NqRs:OS:uV:wWZ:")) != EOF) {
> +	while ((c = getopt(argc, argv, "Ab:BCdDf:Fi:NqRs:OS:uUV:wWZ:")) != EOF) {
>  		switch (c) {
>  		case 'b':
>  			tmp = cvtnum(fsblocksize, fssectsize, optarg);
> @@ -328,6 +329,9 @@ pwrite_f(
>  		case 'A':
>  			pwritev2_flags |= RWF_ATOMIC;
>  			break;
> +		case 'U':
> +			pwritev2_flags |= RWF_DONTCACHE;
> +			break;
>  #endif
>  		case 's':
>  			skip = cvtnum(fsblocksize, fssectsize, optarg);
> @@ -392,6 +396,12 @@ pwrite_f(
>  		exitcode = 1;
>  		return command_usage(&pwrite_cmd);
>  	}
> +	if (pwritev2_flags != 0 && vectors == 0) {
> +		printf(_("pwritev2 flags require vectored I/O (-V)\n"));
> +		exitcode = 1;
> +		return command_usage(&pwrite_cmd);
> +	}
> +
>  	offset = cvtnum(fsblocksize, fssectsize, argv[optind]);
>  	if (offset < 0) {
>  		printf(_("non-numeric offset argument -- %s\n"), argv[optind]);
> @@ -480,7 +490,7 @@ pwrite_init(void)
>  	pwrite_cmd.argmax = -1;
>  	pwrite_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK;
>  	pwrite_cmd.args =
> -_("[-i infile [-qAdDwNOW] [-s skip]] [-b bs] [-S seed] [-FBR [-Z N]] [-V N] off len");
> +_("[-i infile [-qAdDwNOUW] [-s skip]] [-b bs] [-S seed] [-FBR [-Z N]] [-V N] off len");
>  	pwrite_cmd.oneline =
>  		_("writes a number of bytes at a specified offset");
>  	pwrite_cmd.help = pwrite_help;
> diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
> index 59d5ddc5..47af5232 100644
> --- a/man/man8/xfs_io.8
> +++ b/man/man8/xfs_io.8
> @@ -244,7 +244,7 @@ See the
>  .B pread
>  command.
>  .TP
> -.BI "pwrite [ \-i " file " ] [ \-qAdDwNOW ] [ \-s " skip " ] [ \-b " size " ] [ \-S " seed " ] [ \-FBR [ \-Z " zeed " ] ] [ \-V " vectors " ] " "offset length"
> +.BI "pwrite [ \-i " file " ] [ \-qAdDwNOUW ] [ \-s " skip " ] [ \-b " size " ] [ \-S " seed " ] [ \-FBR [ \-Z " zeed " ] ] [ \-V " vectors " ] " "offset length"
>  Writes a range of bytes in a specified blocksize from the given
>  .IR offset .
>  The bytes written can be either a set pattern or read in from another
> @@ -287,6 +287,12 @@ Perform the
>  call with
>  .IR RWF_ATOMIC .
>  .TP
> +.B \-U
> +Perform the
> +.BR pwritev2 (2)
> +call with
> +.IR RWF_DONTCACHE .
> +.TP
>  .B \-O
>  perform pwrite once and return the (maybe partial) bytes written.
>  .TP
> -- 
> 2.48.1
> 
>