[PATCH 1/2] block/file-posix: Fix problem with fallocate(PUNCH_HOLE) on GPFS

[Thomas Huth <thuth@redhat.com>]

A customer reported that running

 qemu-img convert -t none -O qcow2 -f qcow2 input.qcow2 output.qcow2

fails for them with the following error message when the images are
stored on a GPFS file system :

 qemu-img: error while writing sector 0: Invalid argument

After analyzing the strace output, it seems like the problem is in
handle_aiocb_write_zeroes(): The call to fallocate(FALLOC_FL_PUNCH_HOLE)
returns EINVAL, which can apparently happen if the file system has
a different idea of the granularity of the operation. It's arguably
a bug in GPFS, since the PUNCH_HOLE mode should not result in EINVAL
according to the man-page of fallocate(), but the file system is out
there in production and so we have to deal with it. In commit 294682cc3a
("block: workaround for unaligned byte range in fallocate()") we also
already applied the a work-around for the same problem to the earlier
fallocate(FALLOC_FL_ZERO_RANGE) call, so do it now similar with the
PUNCH_HOLE call. But instead of silently catching and returning
-ENOTSUP (which causes the caller to fall back to writing zeroes),
let's rather inform the user once about the buggy file system and
try the other fallback instead.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 block/file-posix.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/block/file-posix.c b/block/file-posix.c
index 10b71d9a13..134ff01d82 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1650,6 +1650,16 @@ static int handle_aiocb_write_zeroes(void *opaque)
                 return ret;
             }
             s->has_fallocate = false;
+        } else if (ret == -EINVAL) {
+            /*
+             * Some file systems like older versions of GPFS do not like un-
+             * aligned byte ranges, and return EINVAL in such a case, though
+             * they should not do it according to the man-page of fallocate().
+             * Warn about the bad filesystem and try the final fallback instead.
+             */
+            warn_report_once("Your file system is misbehaving: "
+                             "fallocate(FALLOC_FL_PUNCH_HOLE) returned EINVAL. "
+                             "Please report this bug to your file sytem vendor.");
         } else if (ret != -ENOTSUP) {
             return ret;
         } else {
-- 
2.27.0