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From: | Max Reitz |
Subject: | Re: [Qemu-devel] [PATCH v4 07/10] qcow2: Rebuild refcount structure during check |
Date: | Fri, 29 Aug 2014 21:25:18 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 |
On 28.08.2014 18:08, Benoît Canet wrote:
On Wed, Aug 27, 2014 at 10:18:23PM +0200, Max Reitz wrote:The previous commit introduced the "rebuild" variable to qcow2's implementation of the image consistency check. Now make use of this by adding a function which creates a completely new refcount structure based solely on the in-memory information gathered before. The old refcount structure will be leaked, however. Signed-off-by: Max Reitz <address@hidden> --- block/qcow2-refcount.c | 287 ++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 284 insertions(+), 3 deletions(-) diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 6300cec..2dca6d4 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -1603,6 +1603,267 @@ static void compare_refcounts(BlockDriverState *bs, BdrvCheckResult *res, }/*+ * Allocates a cluster using an in-memory refcount table (IMRT) in contrast to + * the on-disk refcount structures. + * + * *first_free_cluster does not necessarily point to the first free cluster, but + * may point to one cluster as close as possible before it. The offset returned + * will never be before that cluster. + * + * Note that *first_free_cluster is a cluster index whereas the return value is + * an offset. + */ +static int64_t alloc_clusters_imrt(BlockDriverState *bs, + int cluster_count, + uint16_t **refcount_table, + int64_t *nb_clusters, + int64_t *first_free_cluster) +{ + BDRVQcowState *s = bs->opaque; + int64_t cluster = *first_free_cluster, i; + bool first_gap = true; + int contiguous_free_clusters; + + /* Starting at *first_free_cluster, find a range of at least cluster_count + * continuously free clusters */ + for (contiguous_free_clusters = 0; + cluster < *nb_clusters && contiguous_free_clusters < cluster_count; + cluster++) + { + if (!(*refcount_table)[cluster]) { + contiguous_free_clusters++; + if (first_gap) { + /* If this is the first free cluster found, update + * *first_free_cluster accordingly */ + *first_free_cluster = cluster; + first_gap = false; + } + } else if (contiguous_free_clusters) { + contiguous_free_clusters = 0; + } + } + + /* If contiguous_free_clusters is greater than zero, it contains the number + * of continuously free clusters until the current cluster; the first free + * cluster in the current "gap" is therefore + * cluster - contiguous_free_clusters */ + + /* If no such range could be found, grow the in-memory refcount table + * accordingly to append free clusters at the end of the image */ + if (contiguous_free_clusters < cluster_count) { + int64_t old_nb_clusters = *nb_clusters; + + /* There already is a gap of contiguous_free_clusters; we need + * cluster_count clusters; therefore, we have to allocate + * cluster_count - contiguous_free_clusters new clusters at the end of + * the image (which is the current value of cluster; note that cluster + * may exceed old_nb_clusters if *first_free_cluster pointed beyond the + * image end) */ + *nb_clusters = cluster + cluster_count - contiguous_free_clusters; + *refcount_table = g_try_realloc(*refcount_table, + *nb_clusters * sizeof(uint16_t)); + if (!*refcount_table) { + return -ENOMEM; + } + + memset(*refcount_table + old_nb_clusters, 0, + (*nb_clusters - old_nb_clusters) * sizeof(uint16_t)); + } + + /* Go back to the first free cluster */ + cluster -= contiguous_free_clusters; + for (i = 0; i < cluster_count; i++) { + (*refcount_table)[cluster + i] = 1; + } + + return cluster << s->cluster_bits; +} + +/* + * Creates a new refcount structure based solely on the in-memory information + * given through *refcount_table. All necessary allocations will be reflected + * in that array. + * + * On success, the old refcount structure is leaked (it will be covered by the + * new refcount structure). + */ +static int rebuild_refcount_structure(BlockDriverState *bs, + BdrvCheckResult *res, + uint16_t **refcount_table, + int64_t *nb_clusters) +{ + BDRVQcowState *s = bs->opaque; + int64_t first_free_cluster = 0, rt_ofs = -1, cluster = 0; + int64_t rb_ofs, rb_start, rb_index; + uint32_t reftable_size = 0; + uint64_t *reftable = NULL; + uint16_t *on_disk_rb; + uint8_t rt_offset_and_clusters[sizeof(uint64_t) + sizeof(uint32_t)];Could this be a small struct ?
Yes, it most certainly could, but considering there are other places which use this form already (block/qcow2-refcount.c, line 406 (on 8b30301) or block/qcow2-cluster.c, line 40), I think it's not worth it.
+ int i, ret = 0; + + qcow2_cache_empty(bs, s->refcount_block_cache); + +write_refblocks: + for (; cluster < *nb_clusters; cluster++) { + if (!(*refcount_table)[cluster]) { + continue; + } + + rb_index = cluster >> (s->cluster_bits - 1); + rb_start = rb_index << (s->cluster_bits - 1);Do we have an hardcoded hidden relationship to s->refcount_order / sizeof(uint16_t) here ?
You're right, we have. I guess I'll just add a new field to BDRVQcowState named "refblock_shift" or something like that.
+ + /* Don't allocate a cluster in a refblock already written to disk */ + if (first_free_cluster < rb_start) { + first_free_cluster = rb_start; + } + rb_ofs = alloc_clusters_imrt(bs, 1, refcount_table, nb_clusters, + &first_free_cluster); + if (rb_ofs < 0) { + fprintf(stderr, "ERROR allocating refblock: %s\n", strerror(-ret)); + res->check_errors++; + ret = rb_ofs; + goto fail; + } + + if (reftable_size <= rb_index) { + uint32_t old_rt_size = reftable_size; + reftable_size = ROUND_UP((rb_index + 1) * sizeof(uint64_t), + s->cluster_size) / sizeof(uint64_t); + reftable = g_try_realloc(reftable, + reftable_size * sizeof(uint64_t)); + if (!reftable) { + res->check_errors++; + ret = -ENOMEM; + goto fail; + } + + memset(reftable + old_rt_size, 0, + (reftable_size - old_rt_size) * sizeof(uint64_t)); + + /* The offset we have for the reftable is now no longer valid; + * this will leak that range, but we can easily fix that by running + * a leak-fixing check after this rebuild operation */ + rt_ofs = -1; + } + reftable[rb_index] = rb_ofs; + + /* If this is apparently the last refblock (for now), try to squeeze the + * reftable in; 1 << (s->cluster_bits - MAX(0, s->refcount_order - 3)) + * is the number of entries per refblock (1 << s->refcount_order is the + * number of bits per refblock entry, but we need the number of bytes); + * therefore, (*nb_clusters - 1) >> ... is the index of the last + * refblock */ + if (rb_index == (*nb_clusters - 1) >> + (s->cluster_bits - MAX(0, s->refcount_order - 3)) && rt_ofs < 0) + { + rt_ofs = alloc_clusters_imrt(bs, size_to_clusters(s, reftable_size * + sizeof(uint64_t)), + refcount_table, nb_clusters, + &first_free_cluster); + if (rt_ofs < 0) { + fprintf(stderr, "ERROR allocating reftable: %s\n", + strerror(-ret)); + res->check_errors++; + ret = rt_ofs; + goto fail; + } + } + + ret = qcow2_pre_write_overlap_check(bs, 0, rb_ofs, s->cluster_size); + if (ret < 0) { + fprintf(stderr, "ERROR writing refblock: %s\n", strerror(-ret)); + goto fail; + } ++ on_disk_rb = g_malloc0(s->cluster_size);Do we want g_try_malloc0 here ?
There is no real reason not to, but there is also no real reason to. s->cluster_size should be reasonably small so this should never fail. On the other hand, if I'm respinning this anyway, I might as well.
+ for (i = 0; i < s->cluster_size / sizeof(uint16_t) && + rb_start + i < *nb_clusters; i++) + { + on_disk_rb[i] = cpu_to_be16((*refcount_table)[rb_start + i]); + } + + ret = bdrv_write(bs->file, rb_ofs / BDRV_SECTOR_SIZE, + (void *)on_disk_rb, s->cluster_sectors); + g_free(on_disk_rb); + if (ret < 0) { + fprintf(stderr, "ERROR writing refblock: %s\n", strerror(-ret)); + goto fail; + } + + /* Go to the end of this refblock */ + cluster = rb_start + s->cluster_size / sizeof(uint16_t) - 1; + } + + if (rt_ofs < 0) { + int64_t post_rb_start = ROUND_UP(*nb_clusters, + s->cluster_size / sizeof(uint16_t)); + + /* Not pretty but simple */ + if (first_free_cluster < post_rb_start) { + first_free_cluster = post_rb_start; + } + rt_ofs = alloc_clusters_imrt(bs, size_to_clusters(s, reftable_size * + sizeof(uint64_t)), + refcount_table, nb_clusters, + &first_free_cluster); + if (rt_ofs < 0) { + fprintf(stderr, "ERROR allocating reftable: %s\n", strerror(-ret)); + res->check_errors++; + ret = rt_ofs; + goto fail; + } + + goto write_refblocks; + } + + assert(reftable); + + for (rb_index = 0; rb_index < reftable_size; rb_index++) { + cpu_to_be64s(&reftable[rb_index]); + } + + ret = qcow2_pre_write_overlap_check(bs, 0, rt_ofs, + reftable_size * sizeof(uint64_t)); + if (ret < 0) { + fprintf(stderr, "ERROR writing reftable: %s\n", strerror(-ret)); + goto fail; + } + + ret = bdrv_write(bs->file, rt_ofs / BDRV_SECTOR_SIZE, (void *)reftable, + reftable_size * sizeof(uint64_t) / BDRV_SECTOR_SIZE); + if (ret < 0) { + fprintf(stderr, "ERROR writing reftable: %s\n", strerror(-ret)); + goto fail; + } + + /* Enter new reftable into the image header */ + cpu_to_be64w((uint64_t *)&rt_offset_and_clusters[0], rt_ofs); + cpu_to_be32w((uint32_t *)&rt_offset_and_clusters[sizeof(uint64_t)], + size_to_clusters(s, reftable_size * sizeof(uint64_t)));Manipulating an utility struct would problably some casts.
Hm... Well, I probably shouldn't use pre-existing bad code as an excuse. Okay, I'll use an anonymous struct.
+ ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, + refcount_table_offset), + rt_offset_and_clusters, + sizeof(rt_offset_and_clusters)); + if (ret < 0) { + fprintf(stderr, "ERROR setting reftable: %s\n", strerror(-ret)); + goto fail; + } + + for (rb_index = 0; rb_index < reftable_size; rb_index++) { + be64_to_cpus(&reftable[rb_index]); + } + s->refcount_table = reftable; + s->refcount_table_offset = rt_ofs; + s->refcount_table_size = reftable_size; + + return 0; + +fail: + g_free(reftable); + return ret; +} + +/* * Checks an image for refcount consistency. * * Returns 0 if no errors are found, the number of errors in case the image is @@ -1612,6 +1873,7 @@ int qcow2_check_refcounts(BlockDriverState *bs, BdrvCheckResult *res, BdrvCheckMode fix) { BDRVQcowState *s = bs->opaque; + BdrvCheckResult pre_compare_res; int64_t size, highest_cluster, nb_clusters; uint16_t *refcount_table = NULL; bool rebuild = false; @@ -1638,11 +1900,30 @@ int qcow2_check_refcounts(BlockDriverState *bs, BdrvCheckResult *res, goto fail; }- compare_refcounts(bs, res, fix, &rebuild, &highest_cluster, refcount_table,+ /* In case we don't need to rebuild the refcount structure (but want to fix + * something), this function is immediately called again, in which case the + * result should be ignored */ + pre_compare_res = *res; + compare_refcounts(bs, res, 0, &rebuild, &highest_cluster, refcount_table, nb_clusters);- if (rebuild) {- fprintf(stderr, "ERROR need to rebuild refcount structures\n"); + if (rebuild && (fix & BDRV_FIX_ERRORS)) { + fprintf(stderr, "Rebuilding refcount structure\n"); + ret = rebuild_refcount_structure(bs, res, &refcount_table, + &nb_clusters); + if (ret < 0) { + goto fail; + } + } else if (fix) { + if (rebuild) { + fprintf(stderr, "ERROR need to rebuild refcount structures\n"); + } + + if (res->leaks || res->corruptions) { + *res = pre_compare_res; + compare_refcounts(bs, res, fix, &rebuild, &highest_cluster, + refcount_table, nb_clusters); + } }/* check OFLAG_COPIED */-- 2.1.0I am nitpicking because I have trouble really understanding the code ;)
Nitpicking is far better than a Reviewed-by without much meaning behind it, so I'm glad about it. :-)
Max
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