[PATCH v3 11/12] block: add bdrv_is_file_on_fuse helper

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

Add a function to check, is it a file-posix node on top of file in
FUSE file system.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 include/block/block.h |  2 ++
 block/file-posix.c    | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/block/block.h b/include/block/block.h
index 877fda06a4..51e957f6fb 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -787,4 +787,6 @@ int coroutine_fn bdrv_co_copy_range(BdrvChild *src, uint64_t src_offset,
                                     BdrvChild *dst, uint64_t dst_offset,
                                     uint64_t bytes, BdrvRequestFlags read_flags,
                                     BdrvRequestFlags write_flags);
+
+bool bdrv_is_file_on_fuse(BlockDriverState *bs);
 #endif
diff --git a/block/file-posix.c b/block/file-posix.c
index 560d1c0a94..4100b8dc89 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -324,6 +324,27 @@ static bool dio_byte_aligned(int fd)
     return false;
 }
 
+static bool is_fuse(int fd)
+{
+#ifdef __linux__
+    struct statfs buf;
+    int ret;
+
+    ret = fstatfs(fd, &buf);
+    if (ret == 0 && buf.f_type == FUSE_SUPER_MAGIC) {
+        return true;
+    }
+#endif
+    return false;
+}
+
+bool bdrv_is_file_on_fuse(BlockDriverState *bs)
+{
+    BDRVRawState *s = bs->opaque;
+
+    return !strcmp(bs->drv->format_name, "file") && is_fuse(s->fd);
+}
+
 /* Check if read is allowed with given memory buffer and length.
  *
  * This function is used to check O_DIRECT memory buffer and request alignment.
-- 
2.18.0