[Qemu-devel] Subject: [PATCH] qcow2 resize with snapshot

[zhangzhiming]

qcow2 resize with snapshot, i modify the code of shrink size.
and some changes for stable and vm state l1 index. thanks for review.



Signed-off-by: zhangzhiming <address@hidden <mailto:address@hidden>>
---
block.c                |   19 ----------------
block/qcow2-cluster.c  |   55 ++++++++++++++++++++++++++++++++++--------------
block/qcow2-snapshot.c |   34 ++++++++++++++--------------
block/qcow2.c          |    2 +-
block/qcow2.h          |    2 +-
5 files changed, 58 insertions(+), 54 deletions(-)

diff --git a/block.c b/block.c
index 0de7b2d..f54bc25 100644
--- a/block.c
+++ b/block.c
@@ -2586,25 +2586,6 @@ int bdrv_truncate(BlockDriverState *bs, int64_t offset)
    return ret;
}

-int bdrv_apply_snapshot(BlockDriverState *bs, const char *snapshot_id,
-                        uint64_t snapshot_size)
-{
-    int ret = bdrv_snapshot_goto(bs, snapshot_id);
-    if (ret < 0) {
-        return ret;
-    }
-
-    ret = refresh_total_sectors(bs, snapshot_size >> BDRV_SECTOR_BITS);
-    if (ret < 0) {
-        return ret;
-    }
-    bdrv_dirty_bitmap_truncate(bs);
-    if (bs->blk) {
-        blk_dev_resize_cb(bs->blk);
-    }
-    return ret;
-}
-
/**
 * Length of a allocated file in bytes. Sparse files are counted by actual
 * allocated space. Return < 0 if error or unknown.
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index ebadddf..2190528 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -32,32 +32,55 @@
#include "qemu/bswap.h"
#include "trace.h"

-int shrink_l1_table(BlockDriverState *bs, int64_t new_l1_size)
+static int free_some_l2_table(BlockDriverState *bs, int64_t old_size,
+                              int64_t new_size)
{
    BDRVQcow2State *s = bs->opaque;
-    int64_t old_l1_size = s->l1_size;
-    s->l1_size = new_l1_size;
-    int ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
-                                             s->l1_size, 1);
-    if (ret < 0) {
-        return ret;
+    int old_l1_size = size_to_l1(s, old_size);
+    int new_l1_size = size_to_l1(s, new_size);
+    if (old_l1_size == new_l1_size) {
+        return 0;
    }
+    int i;
+    for (i = new_l1_size; i < old_l1_size; i++) {
+        uint64_t l2_offset = s->l1_table[i] & L1E_OFFSET_MASK;
+        qcow2_free_clusters(bs, l2_offset, s->cluster_size,
+                            QCOW2_DISCARD_OTHER);
+        s->l1_table[i] = 0;
+        /* write l1 entry will be called for several times and
+         * because l1 is short, i think is tolerated! */
+        qcow2_write_l1_entry(bs, i);
+    }
+    return 0;
+}

-    s->l1_size = old_l1_size;
-    ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
-                                         s->l1_size, -1);
+int shrink_disk(BlockDriverState *bs, int64_t new_size)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int64_t old_size = bs->total_sectors * 512;
+    int64_t new_sector_nb = DIV_ROUND_UP(new_size, 512);
+    int64_t discard_sectors_nb = bs->total_sectors - new_sector_nb;
+    int64_t old_cluster_nb = DIV_ROUND_UP(old_size, s->cluster_size);
+    int64_t new_cluster_nb = DIV_ROUND_UP(new_size, s->cluster_size);
+    if (old_cluster_nb == new_cluster_nb) {
+        return 0;
+    }
+    s->l1_size = size_to_l1(s, new_size);
+    bs->total_sectors = new_sector_nb;
+    int ret = qcow2_update_header(bs);
    if (ret < 0) {
+        s->l1_size = size_to_l1(s, old_size);
+        bs->total_sectors = old_size / 512;
        return ret;
    }
-    s->l1_size = new_l1_size;

-    uint32_t be_l1_size = cpu_to_be32(s->l1_size);
-    ret = bdrv_pwrite_sync(bs->file->bs, offsetof(QCowHeader, l1_size),
-                           &be_l1_size, sizeof(be_l1_size));
+    /* can't be undone here, if failed nothing will be done */
+    ret = qcow2_discard_clusters(bs, new_size, discard_sectors_nb,
+                                 QCOW2_DISCARD_OTHER, true);
    if (ret < 0) {
-        return ret;
+        return 0;
    }
-
+    free_some_l2_table(bs, old_size, new_size);
    return 0;
}

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 6dd6769..40a0d26 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -490,6 +490,7 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char 
*snapshot_id)

    cur_l1_bytes = s->l1_size * sizeof(uint64_t);
    sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
+    int max_l1_size_bytes = MAX(sn_l1_bytes, cur_l1_bytes);

    /*
     * Copy the snapshot L1 table to the current L1 table.
@@ -499,7 +500,7 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char 
*snapshot_id)
     * Decrease the refcount referenced by the old one only when the L1
     * table is overwritten.
     */
-    sn_l1_table = g_try_malloc0(sn_l1_bytes);
+    sn_l1_table = g_try_malloc0(max_l1_size_bytes);
    if (sn_l1_bytes && sn_l1_table == NULL) {
        ret = -ENOMEM;
        goto fail;
@@ -517,34 +518,32 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char 
*snapshot_id)
        goto fail;
    }

-    ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
-                                        s->l1_table_offset, sn_l1_bytes);
-    if (ret < 0) {
-        goto fail;
-    }
-
-    ret = bdrv_pwrite_sync(bs->file->bs, s->l1_table_offset, sn_l1_table,
-                           sn_l1_bytes);
+    /* update meta data first, for failed */
+    int old_l1_size = s->l1_size;
+    uint64_t old_total_sectors = bs->total_sectors;
+    bs->total_sectors = sn->disk_size / BDRV_SECTOR_SIZE;
+    s->l1_size = sn->l1_size;
+    ret = qcow2_update_header(bs);
    if (ret < 0) {
+        s->l1_size = old_l1_size;
+        bs->total_sectors = old_total_sectors;
        goto fail;
    }

-    /* write updated header.size */
-    uint64_t be_disk_size = cpu_to_be64(sn->disk_size);
-    ret = bdrv_pwrite_sync(bs->file->bs, offsetof(QCowHeader, size),
-                           &be_disk_size, sizeof(uint64_t));
+    /* and then update l1 table */
+    ret = qcow2_pre_write_overlap_check(bs, QCOW2_OL_ACTIVE_L1,
+                                        s->l1_table_offset, max_l1_size_bytes);
    if (ret < 0) {
        goto fail;
    }

-    uint32_t be_l1_size = cpu_to_be32(sn->l1_size);
-    ret = bdrv_pwrite_sync(bs->file->bs, offsetof(QCowHeader, l1_size),
-                           &be_l1_size, sizeof(be_l1_size));
+    ret = bdrv_pwrite_sync(bs->file->bs, s->l1_table_offset, sn_l1_table,
+                           max_l1_size_bytes);
    if (ret < 0) {
        goto fail;
    }

-    s->l1_vm_state_index = sn->l1_size;
+    s->l1_vm_state_index = size_to_l1(s, sn->disk_size);;

    /*
     * Decrease refcount of clusters of current L1 table.
@@ -556,6 +555,7 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char 
*snapshot_id)
     * the in-memory data instead of really using the offset to load a new one,
     * which is why this works.
     */
+    s->l1_size = old_l1_size;
    ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
                                         s->l1_size, -1);

diff --git a/block/qcow2.c b/block/qcow2.c
index 612a534..01a66f2 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2513,7 +2513,7 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t 
offset)

    new_l1_size = size_to_l1(s, offset);
    if (offset < bs->total_sectors * 512) {
-        ret = shrink_l1_table(bs, new_l1_size);
+        ret = shrink_disk(bs, offset);
        if (ret < 0) {
            return ret;
        }
diff --git a/block/qcow2.h b/block/qcow2.h
index 8efa735..ba622b6 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -534,7 +534,7 @@ int qcow2_change_refcount_order(BlockDriverState *bs, int 
refcount_order,
                                void *cb_opaque, Error **errp);

/* qcow2-cluster.c functions */
-int shrink_l1_table(BlockDriverState *bs, int64_t new_l1_size);
+int shrink_disk(BlockDriverState *bs, int64_t new_size);
int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
                        bool exact_size);
int qcow2_write_l1_entry(BlockDriverState *bs, int l1_index);
-- 
1.7.1




zhangzhiming
address@hidden <mailto:address@hidden>