| Submitter | Kevin Wolf |
|---|---|
| Date | Jan. 18, 2010, 12:11 p.m. |
| Message ID | <1263816696-24122-8-git-send-email-kwolf@redhat.com> |
| Download | mbox | patch |
| Permalink | /patch/43065/ |
| State | New |
| Headers | show |
Comments
On Mon, Jan 18, 2010 at 01:11:33PM +0100, Kevin Wolf wrote: > If update_refcount fails, try to undo any changes made so far to avoid > inconsistencies in the image file. > > Signed-off-by: Kevin Wolf <kwolf@redhat.com> > --- > block/qcow2-refcount.c | 32 +++++++++++++++++++++++++------- > 1 files changed, 25 insertions(+), 7 deletions(-) > > + /* > + * Try do undo any updates if an error is returned (This may succeed in > + * some cases like ENOSPC for allocating a new refcount block) > + */ > + if (ret < 0) { > + int dummy; > + dummy = update_refcount(bs, offset, cluster_offset - offset, -addend); So we recursively call into update_refcount here. What happens an error causes all updates to fail?
Am 19.01.2010 19:51, schrieb Christoph Hellwig: > On Mon, Jan 18, 2010 at 01:11:33PM +0100, Kevin Wolf wrote: >> If update_refcount fails, try to undo any changes made so far to avoid >> inconsistencies in the image file. >> >> Signed-off-by: Kevin Wolf <kwolf@redhat.com> >> --- >> block/qcow2-refcount.c | 32 +++++++++++++++++++++++++------- >> 1 files changed, 25 insertions(+), 7 deletions(-) >> > >> + /* >> + * Try do undo any updates if an error is returned (This may succeed in >> + * some cases like ENOSPC for allocating a new refcount block) >> + */ >> + if (ret < 0) { >> + int dummy; >> + dummy = update_refcount(bs, offset, cluster_offset - offset, -addend); > > So we recursively call into update_refcount here. What happens an error > causes all updates to fail? We're only reverting writes that have succeeded. If reverting fails, there are no successful writes and update_refcount will be called with a length of 0 (which never fails). In the worst case we're only reverting one cluster less with each recursive call - however, I don't think that's a realistic scenario. Kevin
Patch
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 6f449c6..a84620f 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -278,6 +278,7 @@ static int update_refcount(BlockDriverState *bs, int64_t refcount_block_offset = 0; int64_t table_index = -1, old_table_index; int first_index = -1, last_index = -1; + int ret; #ifdef DEBUG_ALLOC2 printf("update_refcount: offset=%" PRId64 " size=%" PRId64 " addend=%d\n", @@ -292,6 +293,7 @@ static int update_refcount(BlockDriverState *bs, { int block_index, refcount; int64_t cluster_index = cluster_offset >> s->cluster_bits; + int64_t new_block; /* Only write refcount block to disk when we are done with it */ old_table_index = table_index; @@ -309,10 +311,12 @@ static int update_refcount(BlockDriverState *bs, } /* Load the refcount block and allocate it if needed */ - refcount_block_offset = alloc_refcount_block(bs, cluster_index); - if (refcount_block_offset < 0) { - return refcount_block_offset; + new_block = alloc_refcount_block(bs, cluster_index); + if (new_block < 0) { + ret = new_block; + goto fail; } + refcount_block_offset = new_block; /* we can update the count and save it */ block_index = cluster_index & @@ -326,24 +330,38 @@ static int update_refcount(BlockDriverState *bs, refcount = be16_to_cpu(s->refcount_block_cache[block_index]); refcount += addend; - if (refcount < 0 || refcount > 0xffff) - return -EINVAL; + if (refcount < 0 || refcount > 0xffff) { + ret = -EINVAL; + goto fail; + } if (refcount == 0 && cluster_index < s->free_cluster_index) { s->free_cluster_index = cluster_index; } s->refcount_block_cache[block_index] = cpu_to_be16(refcount); } + ret = 0; +fail: + /* Write last changed block to disk */ if (refcount_block_offset != 0) { if (write_refcount_block_entries(s, refcount_block_offset, first_index, last_index) < 0) { - return -EIO; + return ret < 0 ? ret : -EIO; } } - return 0; + /* + * Try do undo any updates if an error is returned (This may succeed in + * some cases like ENOSPC for allocating a new refcount block) + */ + if (ret < 0) { + int dummy; + dummy = update_refcount(bs, offset, cluster_offset - offset, -addend); + } + + return ret; } /* addend must be 1 or -1 */
If update_refcount fails, try to undo any changes made so far to avoid inconsistencies in the image file. Signed-off-by: Kevin Wolf <kwolf@redhat.com> --- block/qcow2-refcount.c | 32 +++++++++++++++++++++++++------- 1 files changed, 25 insertions(+), 7 deletions(-)