On 2025/8/15 0:54, Darrick J. Wong wrote:
> On Wed, Aug 13, 2025 at 10:42:50AM +0800, Zhang Yi wrote:
>> From: Zhang Yi <yi.zh...@huawei.com>
>>
>> The Linux kernel (since version 6.17) supports FALLOC_FL_WRITE_ZEROES in
>> fallocate(2). Add support for FALLOC_FL_WRITE_ZEROES support to the
>> fallocate utility by introducing a new 'fwzero' command in the xfs_io
>> tool.
>>
>> Link: 
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=278c7d9b5e0c
>> Signed-off-by: Zhang Yi <yi.zh...@huawei.com>
>> ---
>> v1->v2:
>>  - Minor description modification to align with the kernel.
>>
>>  io/prealloc.c     | 36 ++++++++++++++++++++++++++++++++++++
>>  man/man8/xfs_io.8 |  6 ++++++
>>  2 files changed, 42 insertions(+)
>>
>> diff --git a/io/prealloc.c b/io/prealloc.c
>> index 8e968c9f..9a64bf53 100644
>> --- a/io/prealloc.c
>> +++ b/io/prealloc.c
>> @@ -30,6 +30,10 @@
>>  #define FALLOC_FL_UNSHARE_RANGE 0x40
>>  #endif
>>  
>> +#ifndef FALLOC_FL_WRITE_ZEROES
>> +#define FALLOC_FL_WRITE_ZEROES 0x80
>> +#endif
>> +
>>  static cmdinfo_t allocsp_cmd;
>>  static cmdinfo_t freesp_cmd;
>>  static cmdinfo_t resvsp_cmd;
>> @@ -41,6 +45,7 @@ static cmdinfo_t fcollapse_cmd;
>>  static cmdinfo_t finsert_cmd;
>>  static cmdinfo_t fzero_cmd;
>>  static cmdinfo_t funshare_cmd;
>> +static cmdinfo_t fwzero_cmd;
>>  
>>  static int
>>  offset_length(
>> @@ -377,6 +382,27 @@ funshare_f(
>>      return 0;
>>  }
>>  
>> +static int
>> +fwzero_f(
>> +    int             argc,
>> +    char            **argv)
>> +{
>> +    xfs_flock64_t   segment;
>> +    int             mode = FALLOC_FL_WRITE_ZEROES;
> 
> Shouldn't this take a -k to add FALLOC_FL_KEEP_SIZE like fzero?
> 

Since allocating blocks with written extents beyond the inode size
is not permitted, the FALLOC_FL_WRITE_ZEROES flag cannot be used
together with the FALLOC_FL_KEEP_SIZE.

Thanks,
Yi.

> (The code otherwise looks fine to me)
> 
> --D
> 
>> +
>> +    if (!offset_length(argv[1], argv[2], &segment)) {
>> +            exitcode = 1;
>> +            return 0;
>> +    }
>> +
>> +    if (fallocate(file->fd, mode, segment.l_start, segment.l_len)) {
>> +            perror("fallocate");
>> +            exitcode = 1;
>> +            return 0;
>> +    }
>> +    return 0;
>> +}
>> +
>>  void
>>  prealloc_init(void)
>>  {
>> @@ -489,4 +515,14 @@ prealloc_init(void)
>>      funshare_cmd.oneline =
>>      _("unshares shared blocks within the range");
>>      add_command(&funshare_cmd);
>> +
>> +    fwzero_cmd.name = "fwzero";
>> +    fwzero_cmd.cfunc = fwzero_f;
>> +    fwzero_cmd.argmin = 2;
>> +    fwzero_cmd.argmax = 2;
>> +    fwzero_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK;
>> +    fwzero_cmd.args = _("off len");
>> +    fwzero_cmd.oneline =
>> +    _("zeroes space and eliminates holes by allocating and submitting write 
>> zeroes");
>> +    add_command(&fwzero_cmd);
>>  }
>> diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
>> index b0dcfdb7..0a673322 100644
>> --- a/man/man8/xfs_io.8
>> +++ b/man/man8/xfs_io.8
>> @@ -550,6 +550,12 @@ With the
>>  .B -k
>>  option, use the FALLOC_FL_KEEP_SIZE flag as well.
>>  .TP
>> +.BI fwzero " offset length"
>> +Call fallocate with FALLOC_FL_WRITE_ZEROES flag as described in the
>> +.BR fallocate (2)
>> +manual page to allocate and zero blocks within the range by submitting write
>> +zeroes.
>> +.TP
>>  .BI zero " offset length"
>>  Call xfsctl with
>>  .B XFS_IOC_ZERO_RANGE
>> -- 
>> 2.39.2
>>
>>


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