[Virtio-fs] [PATCH] virtiofsd: do fallocate for setupmapping requests with write flag

[Liu Bo]

We'll have to make sure filesystem has allocated space for the dax
mapping, otherwise, guest writes from virtiofs may hang since write
page fault is not able to be resolved if host fs is full
(->page_mkwrite() return -ENOSPC).

Signed-off-by: Liu Bo <bo.liu at linux.alibaba.com>
---
 contrib/virtiofsd/passthrough_ll.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
index f14f471..1ddb68f 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -1897,12 +1897,28 @@ static void lo_setupmapping(fuse_req_t req, fuse_ino_t ino, uint64_t foffset,
 
 	}
 
+        if (flags & O_WRONLY) {
+                /* this may allocate more space than we need. */
+                ret = fallocate(fd, FALLOC_FL_KEEP_SIZE, foffset, len);
+                if (ret < 0) {
+                        ret = errno;
+                        fprintf(stderr, "%s: fallocate fail (ino=%" PRId64 "fd=%d foffset=0x%" PRIx64 ")\n",
+                                __func__, ino, fi ? (int)fi->fh : lo_fd(req, ino), foffset);
+                        goto err;
+                }
+
+                if (lo_debug(req))
+                        fprintf(stderr, "fallocate (foffset=%" PRIx64 "moffset=%" PRIx64 ")\n",
+                                foffset, moffset);
+        }
+
         if (fuse_virtio_map(req, &msg, fd)) {
                 fprintf(stderr, "%s: map over virtio failed (ino=%" PRId64 "fd=%d moffset=0x%" PRIx64 ")\n",
                         __func__, ino, fi ? (int)fi->fh : lo_fd(req, ino), moffset);
                 ret = EINVAL;
         }
 
+err:
 	if (!fi)
 		close(fd);
 	fuse_reply_err(req, ret);
-- 
1.8.3.1