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

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

"Darrick J. Wong" <djwong@kernel.org> writes:

> 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.
>

Yes, probably I was just overthinking and trying to give a reason here of
choosing -U (Uncached). 

> With that shortened, this looks pretty straightforward.

Sure will fix in v3.

> Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

Thanks!

-ritesh

>
> --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
>> 
>>