[Qemu-devel] [PATCH] block/raw-posix: Fall back to SEEK_HOLE/SEEK_DATA

[Max Reitz]

The current version of raw-posix always uses ioctl(FS_IOC_FIEMAP) if
FIEMAP is available; lseek with SEEK_HOLE/SEEK_DATA are not even
compiled in in this case. However, there may be implementations which
support the latter but not the former (e.g., NFSv4.2). In this case,
raw-posix should fall back to lseek with SEEK_HOLE/SEEK_DATA if FIEMAP
does not work.

Signed-off-by: Max Reitz <address@hidden>
---
As Linux does not yet implement NFSv4.2 (I don't even know whether the
specification is complete), I have no way of testing whether this
actually works for the proposed case. But as it doesn't break any of the
existing test cases, it should be fine.
---
 block/raw-posix.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/block/raw-posix.c b/block/raw-posix.c
index 3ce026d..e523633 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -146,6 +146,9 @@ typedef struct BDRVRawState {
     bool has_discard:1;
     bool has_write_zeroes:1;
     bool discard_zeroes:1;
+#if defined CONFIG_FIEMAP && defined SEEK_HOLE && defined SEEK_DATA
+    bool use_seek_hole_data;
+#endif
 } BDRVRawState;
 
 typedef struct BDRVRawReopenState {
@@ -1291,6 +1294,7 @@ static int64_t coroutine_fn 
raw_co_get_block_status(BlockDriverState *bs,
                                             int64_t sector_num,
                                             int nb_sectors, int *pnum)
 {
+    BDRVRawState *s = bs->opaque;
     off_t start, data, hole;
     int64_t ret;
 
@@ -1303,22 +1307,31 @@ static int64_t coroutine_fn 
raw_co_get_block_status(BlockDriverState *bs,
     ret = BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | start;
 
 #ifdef CONFIG_FIEMAP
-
-    BDRVRawState *s = bs->opaque;
     struct {
         struct fiemap fm;
         struct fiemap_extent fe;
     } f;
 
+#if defined SEEK_HOLE && defined SEEK_DATA
+    if (s->use_seek_hole_data) {
+        goto try_seek_hole_data;
+    }
+#endif
+
     f.fm.fm_start = start;
     f.fm.fm_length = (int64_t)nb_sectors * BDRV_SECTOR_SIZE;
     f.fm.fm_flags = 0;
     f.fm.fm_extent_count = 1;
     f.fm.fm_reserved = 0;
     if (ioctl(s->fd, FS_IOC_FIEMAP, &f) == -1) {
+#if defined SEEK_HOLE && defined SEEK_DATA
+        s->use_seek_hole_data = true;
+        goto try_seek_hole_data;
+#else
         /* Assume everything is allocated.  */
         *pnum = nb_sectors;
         return ret;
+#endif
     }
 
     if (f.fm.fm_mapped_extents == 0) {
@@ -1336,10 +1349,11 @@ static int64_t coroutine_fn 
raw_co_get_block_status(BlockDriverState *bs,
         }
     }
 
-#elif defined SEEK_HOLE && defined SEEK_DATA
-
-    BDRVRawState *s = bs->opaque;
+    goto done;
+#endif
 
+#if defined SEEK_HOLE && defined SEEK_DATA
+try_seek_hole_data:
     hole = lseek(s->fd, start, SEEK_HOLE);
     if (hole == -1) {
         /* -ENXIO indicates that sector_num was past the end of the file.
@@ -1360,11 +1374,12 @@ static int64_t coroutine_fn 
raw_co_get_block_status(BlockDriverState *bs,
             data = lseek(s->fd, 0, SEEK_END);
         }
     }
-#else
+#elif !defined CONFIG_FIEMAP
     data = 0;
     hole = start + nb_sectors * BDRV_SECTOR_SIZE;
 #endif
 
+done:
     if (data <= start) {
         /* On a data extent, compute sectors to the end of the extent.  */
         *pnum = MIN(nb_sectors, (hole - start) / BDRV_SECTOR_SIZE);
-- 
1.9.2