[Devel] [PATCH rh7] ploop: do not use fiemap beyond eof

[Maxim Patlasov]

From: Maxim Patlasov <MPatlasov at openvz.org>

map_extent_get_block() optimizes I/O by merging adjacent ext4 extents. However,
it's useless to ask ext4 about layout beyond EOF because ploop always extends
image file by fallocate() w/o FALLOC_FL_KEEP_SIZE flag.

And more than that -- it can be also dangerous because userspace merge
utility may race with us extending image file by ordinary write-s resulting
in (temporary) FIEMAP_EXTENT_DELALLOC extents.

https://jira.sw.ru/browse/PSBM-26762
https://jira.sw.ru/browse/PSBM-39251
---
 drivers/block/ploop/io_direct_map.c |    5 +++++
 1 file changed, 5 insertions(+)
-------------- next part --------------
From: Maxim Patlasov <mpatlasov at virtuozzo.com>

map_extent_get_block() optimizes I/O by merging adjacent ext4 extents. However,
it's useless to ask ext4 about layout beyond EOF because ploop always extends
image file by fallocate() w/o FALLOC_FL_KEEP_SIZE flag.

And more than that -- it can be also dangerous because userspace merge
utility may race with us extending image file by ordinary write-s resulting
in (temporary) FIEMAP_EXTENT_DELALLOC extents.

https://jira.sw.ru/browse/PSBM-26762
https://jira.sw.ru/browse/PSBM-39251
---
 drivers/block/ploop/io_direct_map.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/block/ploop/io_direct_map.c b/drivers/block/ploop/io_direct_map.c
index c1d889b..977adc2 100644
--- a/drivers/block/ploop/io_direct_map.c
+++ b/drivers/block/ploop/io_direct_map.c
@@ -776,6 +776,11 @@ struct extent_map *map_extent_get_block(struct ploop_io *io,
 	 * something bigger.
 	 */
 	do {
+		/* avoid race with userspace merge */
+		if (em->end >=
+		    ((sector_t)io->alloc_head << io->plo->cluster_log))
+			break;
+
 		last = em->end;
 		extent_put(em);
 		em = __map_extent(io, mapping, last, len, create,