Re: [PATCH v2 3/3] xfs_io: Add RWF_DONTCACHE support to preadv2

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

On Wed, Mar 05, 2025 at 03:57:48PM +0530, Ritesh Harjani (IBM) wrote:
> Add per-io RWF_DONTCACHE support flag to preadv2().
> This enables xfs_io to perform uncached buffered-io reads.
> 
> 	e.g. xfs_io -c "pread -U -V 1 0 16K" /mnt/f1
> 
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> ---
>  io/pread.c        | 17 +++++++++++++++--
>  man/man8/xfs_io.8 |  8 +++++++-
>  2 files changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/io/pread.c b/io/pread.c
> index b314fbc7..79e6570e 100644
> --- a/io/pread.c
> +++ b/io/pread.c
> @@ -38,6 +38,9 @@ pread_help(void)
>  " -Z N -- zeed the random number generator (used when reading randomly)\n"
>  "         (heh, zorry, the -s/-S arguments were already in use in pwrite)\n"
>  " -V N -- use vectored IO with N iovecs of blocksize each (preadv)\n"
> +#ifdef HAVE_PREADV2
> +" -U   -- Perform the preadv2() with Uncached/RWF_DONTCACHE\n"

Same comment as the last patch, but otherwise this looks good;
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> +#endif
>  "\n"
>  " When in \"random\" mode, the number of read operations will equal the\n"
>  " number required to do a complete forward/backward scan of the range.\n"
> @@ -388,7 +391,7 @@ pread_f(
>  	init_cvtnum(&fsblocksize, &fssectsize);
>  	bsize = fsblocksize;
>  
> -	while ((c = getopt(argc, argv, "b:BCFRquvV:Z:")) != EOF) {
> +	while ((c = getopt(argc, argv, "b:BCFRquUvV:Z:")) != EOF) {
>  		switch (c) {
>  		case 'b':
>  			tmp = cvtnum(fsblocksize, fssectsize, optarg);
> @@ -417,6 +420,11 @@ pread_f(
>  		case 'u':
>  			uflag = 1;
>  			break;
> +#ifdef HAVE_PREADV2
> +		case 'U':
> +			preadv2_flags |= RWF_DONTCACHE;
> +			break;
> +#endif
>  		case 'v':
>  			vflag = 1;
>  			break;
> @@ -446,6 +454,11 @@ pread_f(
>  		exitcode = 1;
>  		return command_usage(&pread_cmd);
>  	}
> +	if (preadv2_flags != 0 && vectors == 0) {
> +		printf(_("preadv2 flags require vectored I/O (-V)\n"));
> +		exitcode = 1;
> +		return command_usage(&pread_cmd);
> +	}
>  
>  	offset = cvtnum(fsblocksize, fssectsize, argv[optind]);
>  	if (offset < 0 && (direction & (IO_RANDOM|IO_BACKWARD))) {
> @@ -514,7 +527,7 @@ pread_init(void)
>  	pread_cmd.argmin = 2;
>  	pread_cmd.argmax = -1;
>  	pread_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK;
> -	pread_cmd.args = _("[-b bs] [-qv] [-i N] [-FBR [-Z N]] off len");
> +	pread_cmd.args = _("[-b bs] [-qUv] [-i N] [-FBR [-Z N]] off len");
>  	pread_cmd.oneline = _("reads a number of bytes at a specified offset");
>  	pread_cmd.help = pread_help;
>  
> diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
> index 47af5232..df508054 100644
> --- a/man/man8/xfs_io.8
> +++ b/man/man8/xfs_io.8
> @@ -200,7 +200,7 @@ option will set the file permissions to read-write (0644). This allows xfs_io to
>  set up mismatches between the file permissions and the open file descriptor
>  read/write mode to exercise permission checks inside various syscalls.
>  .TP
> -.BI "pread [ \-b " bsize " ] [ \-qv ] [ \-FBR [ \-Z " seed " ] ] [ \-V " vectors " ] " "offset length"
> +.BI "pread [ \-b " bsize " ] [ \-qUv ] [ \-FBR [ \-Z " seed " ] ] [ \-V " vectors " ] " "offset length"
>  Reads a range of bytes in a specified blocksize from the given
>  .IR offset .
>  .RS 1.0i
> @@ -214,6 +214,12 @@ requests will be split. The default blocksize is 4096 bytes.
>  .B \-q
>  quiet mode, do not write anything to standard output.
>  .TP
> +.B \-U
> +Perform the
> +.BR preadv2 (2)
> +call with
> +.IR RWF_DONTCACHE .
> +.TP
>  .B \-v
>  dump the contents of the buffer after reading,
>  by default only the count of bytes actually read is dumped.
> -- 
> 2.48.1
> 
>