[PATCH V3] xfsprogs: remove platform_zero_range wrapper

[Eric Sandeen <sandeen@xxxxxxxxxxx>]

Now that the HAVE_FALLOCATE guard around including
<linux/falloc.h> in linux/xfs.h has been removed via
15fb447f ("configure: don't check for fallocate"),
bad things can happen because we reference fallocate in
<xfs/linux.h> without defining _GNU_SOURCE:

$ cat test.c
#include <xfs/linux.h>

int main(void)
{
	return 0;
}

$ gcc -o test test.c
In file included from test.c:1:
/usr/include/xfs/linux.h: In function ‘platform_zero_range’:
/usr/include/xfs/linux.h:186:15: error: implicit declaration of function ‘fallocate’ [-Wimplicit-function-declaration]
  186 |         ret = fallocate(fd, FALLOC_FL_ZERO_RANGE, start, len);
      |               ^~~~~~~~~

i.e. xfs/linux.h includes fcntl.h without _GNU_SOURCE, so we
don't get an fallocate prototype.

Rather than playing games with header files, just remove the
platform_zero_range() wrapper - we have only one platform, and
only one caller after all - and simply call fallocate directly
if we have the FALLOC_FL_ZERO_RANGE flag defined.

(LTP also runs into this sort of problem at configure time ...)

Darrick points out that this changes a public header, but
platform_zero_range() has only been exposed by default
(without the oddball / internal xfsprogs guard) for a couple
of xfsprogs releases, so it's quite unlikely that anyone is
using this oddball fallocate wrapper.

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---

V2: remove error variable, add to commit msg
V3: Drop FALLOC_FL_ZERO_RANGE #ifdef per hch's suggestion and
    add his RVB from V2, with changes.

NOTE: compile tested only

diff --git a/include/linux.h b/include/linux.h
index 95a0deee..a13072d2 100644
--- a/include/linux.h
+++ b/include/linux.h
@@ -174,24 +174,6 @@ 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)
-{
-	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)	(-EOPNOTSUPP)
-#endif
-
 /*
  * Use SIGKILL to simulate an immediate program crash, without a chance to run
  * atexit handlers.
diff --git a/libxfs/rdwr.c b/libxfs/rdwr.c
index 153007d5..b54505b5 100644
--- a/libxfs/rdwr.c
+++ b/libxfs/rdwr.c
@@ -73,7 +73,7 @@ libxfs_device_zero(struct xfs_buftarg *btp, xfs_daddr_t start, uint len)
 
 	/* try to use special zeroing methods, fall back to writes if needed */
 	len_bytes = LIBXFS_BBTOOFF64(len);
-	error = platform_zero_range(fd, start_offset, len_bytes);
+	error = fallocate(fd, FALLOC_FL_ZERO_RANGE, start_offset, len_bytes);
 	if (!error) {
 		xfs_buftarg_trip_write(btp);
 		return 0;