Commit e6d7ec32 authored Oct 24, 2014 by Max Reitz Committed by Stefan Hajnoczi Nov 03, 2014

raw-posix: Fix raw_co_get_block_status() after EOF



As its comment states, raw_co_get_block_status() should unconditionally
return 0 and set *pnum to 0 for after EOF.

An assertion after lseek(..., SEEK_HOLE) tried to catch this case by
asserting that errno != -ENXIO (which would indicate a position after
the EOF); but it should be errno != ENXIO instead. Regardless of that,
there should be no such assertion at all. If bdrv_getlength() returned
an outdated value and the image has been resized outside of qemu,
lseek() will return with errno == ENXIO. Just return that value as an
error then.

Setting *pnum to 0 and returning 0 should not be done here, as in that
case we should update the device length as well. So, from qemu's
perspective, the file has not been resized; it's just that there was an
error querying sectors beyond a certain point (the actual file size).

Additionally, nb_sectors should be clamped against the image end. This
was probably not an issue if FIEMAP or SEEK_HOLE/SEEK_DATA worked, but
the fallback did not take this case into account.

Reported-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 1414148280-17949-2-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

parent f76faeda

block/raw-posix.c

+10 −4

Original line number	Diff line number	Diff line
		@@ -1535,10 +1535,6 @@ static int64_t try_seek_hole(BlockDriverState bs, off_t start, off_t data,

		*hole = lseek(s->fd, start, SEEK_HOLE);
		if (*hole == -1) {
		/* -ENXIO indicates that sector_num was past the end of the file.
		* There is a virtual hole there. */
		assert(errno != -ENXIO);

		return -errno;
		}

		@@ -1578,6 +1574,7 @@ static int64_t coroutine_fn raw_co_get_block_status(BlockDriverState *bs,
		int nb_sectors, int *pnum)
		{
		off_t start, data = 0, hole = 0;
		int64_t total_size;
		int64_t ret;

		ret = fd_open(bs);
		@@ -1586,6 +1583,15 @@ static int64_t coroutine_fn raw_co_get_block_status(BlockDriverState *bs,
		}

		start = sector_num * BDRV_SECTOR_SIZE;
		total_size = bdrv_getlength(bs);
		if (total_size < 0) {
		return total_size;
		} else if (start >= total_size) {
		*pnum = 0;
		return 0;
		} else if (start + nb_sectors * BDRV_SECTOR_SIZE > total_size) {
		nb_sectors = DIV_ROUND_UP(total_size - start, BDRV_SECTOR_SIZE);
		}

		ret = try_seek_hole(bs, start, &data, &hole, pnum);
		if (ret < 0) {