Re: [PATCH V3] libxfs: use FALLOC_FL_ZERO_RANGE in libxfs_device_zero

[Eric Sandeen <sandeen@sandeen.net>]

On 2/22/20 1:24 AM, Darrick J. Wong wrote:
> On Fri, Feb 21, 2020 at 09:22:12PM -0600, Eric Sandeen wrote:
>> I had a request from someone who cared about mkfs speed(!)
>> over a slower network block device to look into using faster
>> zeroing methods, particularly for the log, during mkfs.
>>
>> Using FALLOC_FL_ZERO_RANGE is faster in this case than writing
>> a bunch of zeros across a wire.
>>
>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>> ---
>>
>> V2: Clean up all the nasty stuff I'd flung out there as a wild first
>> cut, thanks Dave.
>>
>> V3: make len_bytes a size_t; leave "end_offset" where it is for the loop
>> use.  It's a bit odd but ... just don't mess with it for now, one patch
>> one change.
>>
>> diff --git a/include/builddefs.in b/include/builddefs.in
>> index 4700b527..1dd27f76 100644
>> --- a/include/builddefs.in
>> +++ b/include/builddefs.in
>> @@ -144,6 +144,9 @@ endif
>>  ifeq ($(HAVE_GETFSMAP),yes)
>>  PCFLAGS+= -DHAVE_GETFSMAP
>>  endif
>> +ifeq ($(HAVE_FALLOCATE),yes)
>> +PCFLAGS += -DHAVE_FALLOCATE
>> +endif
>>  
>>  LIBICU_LIBS = @libicu_LIBS@
>>  LIBICU_CFLAGS = @libicu_CFLAGS@
>> diff --git a/include/linux.h b/include/linux.h
>> index 8f3c32b0..8d5c4584 100644
>> --- a/include/linux.h
>> +++ b/include/linux.h
>> @@ -20,6 +20,10 @@
>>  #include <stdio.h>
>>  #include <asm/types.h>
>>  #include <mntent.h>
>> +#include <fcntl.h>
>> +#if defined(HAVE_FALLOCATE)
>> +#include <linux/falloc.h>
>> +#endif
>>  #ifdef OVERRIDE_SYSTEM_FSXATTR
>>  # define fsxattr sys_fsxattr
>>  #endif
>> @@ -164,6 +168,24 @@ static inline void platform_mntent_close(struct mntent_cursor * cursor)
>>  	endmntent(cursor->mtabp);
>>  }
>>  
>> +#if defined(FALLOC_FL_ZERO_RANGE)
>> +static inline int
>> +platform_zero_range(
>> +	int		fd,
>> +	xfs_off_t	start,
>> +	size_t		len)
> 
> Seems fine to me, though it's unfortunate to cap this at u32.

Hm well I suppose could/should expand it.  This starts out via libxfs_device_zero
as a uint "len" in sectors so it could/should be a bit bigger.

>> +{
>> +	int ret;
>> +
>> +	ret = fallocate(fd, FALLOC_FL_ZERO_RANGE, start, len);
>> +	if (!ret)
>> +		return 0;
>> +	return -errno;
>> +}
>> +#else
>> +#define platform_zero_range(fd, s, l)	(-EOPNOTSUP)
> 
> EOPNOTSUPP (two P's)

Weird not sure how I picked that, though they are equivalent today.

*sigh* V4 I guess.