|
From: | Max Reitz |
Subject: | Re: [Qemu-devel] [PATCH v6 09/11] qcow2: Clean up after refcount rebuild |
Date: | Tue, 21 Oct 2014 17:17:29 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 |
On 2014-10-21 at 17:11, Kevin Wolf wrote:
Am 21.10.2014 um 16:55 hat Max Reitz geschrieben:On 2014-10-21 at 12:16, Max Reitz wrote:On 2014-10-21 at 11:59, Kevin Wolf wrote:Am 20.10.2014 um 16:35 hat Max Reitz geschrieben:Because the old refcount structure will be leaked after having rebuilt it, we need to recalculate the refcounts and run a leak-fixing operation afterwards (if leaks should be fixed at all). Signed-off-by: Max Reitz <address@hidden> Reviewed-by: BenoƮt Canet <address@hidden> --- block/qcow2-refcount.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 75e726b..3730be2 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -1956,12 +1956,47 @@ int qcow2_check_refcounts(BlockDriverState *bs, BdrvCheckResult *res, nb_clusters); if (rebuild && (fix & BDRV_FIX_ERRORS)) { + BdrvCheckResult old_res = *res; + fprintf(stderr, "Rebuilding refcount structure\n"); ret = rebuild_refcount_structure(bs, res, &refcount_table, &nb_clusters); if (ret < 0) { goto fail; } + + res->corruptions = 0; + res->leaks = 0; + + /* Because the old reftable has been exchanged for a new one the + * references have to be recalculated */ + rebuild = false; + memset(refcount_table, 0, nb_clusters * sizeof(uint16_t)); + ret = calculate_refcounts(bs, res, 0, &rebuild, &refcount_table, + &nb_clusters); + if (ret < 0) { + goto fail; + } + + if (fix & BDRV_FIX_LEAKS) { + /* The old refcount structures are now leaked, fix it; the result + * can be ignored */ + pre_compare_res = *res;I would prefer using another local variable here. At the first sight it's not quite clear which references to pre_compare_res correspond to which state.Why not.+ compare_refcounts(bs, res, BDRV_FIX_LEAKS, &rebuild, + &highest_cluster, refcount_table, nb_clusters); + if (rebuild) { + fprintf(stderr, "ERROR rebuilt refcount structure is still " + "broken\n"); + } + *res = pre_compare_res; + } + + if (res->corruptions < old_res.corruptions) { + res->corruptions_fixed += old_res.corruptions - res->corruptions; + } + if (res->leaks < old_res.leaks) { + res->leaks_fixed += old_res.leaks - res->leaks; + }For these numbers to be accurate, don't we need to run compare_refcounts() unconditionally and only make BDRV_FIX_LEAKS conditional?Actually, there is no difference, because at the point of this patch, you cannot use BDRV_FIX_ERRORS without BDRV_FIX_LEAKS. But it'd be more correct, right.Wait, it would not be more correct. The result of the compare_refcounts() call inside of the "if (fix & BDRV_FIX_LEAKS)" conditional block is ignored, its only purpose is to fix leaks resulting from rebuild_refcount_structure(). So the question is whether we should discard the result of that compare_refcounts() call. I think we should. Its sole purpose is to fix leaks due to the rebuilt refcount structures, and qemu-img will double check anyway.Right, the other leaks should have been fixed by rebuilding the refcount structures. So what you're saying is that we could do this: if (res->corruptions < old_res.corruptions) { res->corruptions_fixed += old_res.corruptions - res->corruptions; } assert(res->leaks == 0); res->leaks_fixed = old_res.leaks; If this weren't true, we'd ignore leaked clusters even with BDRV_FIX_LEAKS set.
Okay, so for obvious reasons this is not nice. Well, I don't know what will be worse. Writing the code which takes the leak fix result into account or having to review it. I think I'll just see how many new leaks appeared due to the rebuild and how many of those could not be fixed, and then add that result to res->leaks. That should work out without being too complicated.
Max
[Prev in Thread] | Current Thread | [Next in Thread] |