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Re: [Qemu-block] [PATCH 13/21] qcow2: add .bdrv_store_persistent_dirty_b
From: |
Max Reitz |
Subject: |
Re: [Qemu-block] [PATCH 13/21] qcow2: add .bdrv_store_persistent_dirty_bitmaps() |
Date: |
Mon, 19 Dec 2016 16:14:28 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 |
On 17.12.2016 15:58, Vladimir Sementsov-Ogievskiy wrote:
> 09.12.2016 20:05, Max Reitz wrote:
>> On 22.11.2016 18:26, Vladimir Sementsov-Ogievskiy wrote:
>>> Realize block bitmap storing interface, to allow qcow2 images store
>>> persistent bitmaps.
>>>
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>> ---
>>> block/qcow2-bitmap.c | 451
>>> +++++++++++++++++++++++++++++++++++++++++++++++++++
>>> block/qcow2.c | 1 +
>
> [...]
>
>>> +
>>> +/* store_bitmap_data()
>>> + * Store bitmap to image, filling bitmap table accordingly.
>>> + */
>>> +static uint64_t *store_bitmap_data(BlockDriverState *bs,
>>> + BdrvDirtyBitmap *bitmap,
>>> + uint32_t *bitmap_table_size, Error
>>> **errp)
>>> +{
>>> + int ret;
>>> + BDRVQcow2State *s = bs->opaque;
>>> + int64_t sector;
>>> + uint64_t dsc;
>>> + uint64_t bm_size = bdrv_dirty_bitmap_size(bitmap);
>>> + const char *bm_name = bdrv_dirty_bitmap_name(bitmap);
>>> + uint8_t *buf = NULL;
>>> + BdrvDirtyBitmapIter *dbi;
>>> + uint64_t *tb;
>>> + uint64_t tb_size =
>>> + size_to_clusters(s,
>>> + bdrv_dirty_bitmap_serialization_size(bitmap, 0, bm_size));
>>> +
>>> + if (tb_size > BME_MAX_TABLE_SIZE ||
>>> + tb_size * s->cluster_size > BME_MAX_PHYS_SIZE) {
>> Alignment to the opening parenthesis, please.
>>
>>> + error_setg(errp, "Bitmap '%s' is too big", bm_name);
>>> + return NULL;
>>> + }
>>> +
>>> + tb = g_try_new0(uint64_t, tb_size);
>>> + if (tb == NULL) {
>>> + error_setg(errp, "No memory");
>>> + return NULL;
>>> + }
>>> +
>>> + dbi = bdrv_dirty_iter_new(bitmap, 0);
>>> + buf = g_malloc(s->cluster_size);
>>> + dsc = disk_sectors_in_bitmap_cluster(s, bitmap);
>>> +
>>> + while ((sector = bdrv_dirty_iter_next(dbi)) != -1) {
>>> + uint64_t cluster = sector / dsc;
>>> + uint64_t end, write_size;
>>> + int64_t off;
>>> +
>>> + sector = cluster * dsc;
>>> + end = MIN(bm_size, sector + dsc);
>>> + write_size =
>>> + bdrv_dirty_bitmap_serialization_size(bitmap, sector, end -
>>> sector);
>>> +
>>> + off = qcow2_alloc_clusters(bs, s->cluster_size);
>>> + if (off < 0) {
>>> + error_setg_errno(errp, -off,
>>> + "Failed to allocate clusters for bitmap '%s'",
>>> + bm_name);
>>> + goto fail;
>>> + }
>>> + tb[cluster] = off;
>> Somehow I would feel better with either an assert(cluster < tb_size);
>> here or an assert(bdrv_nb_sectors(bs) / dsc == tb_size); (plus the error
>> handling for bdrv_nb_sectors()) above the loop.
>
> assert((bm_size - 1) / dsc == tb_size - 1) seems ok. and no additional
> error handling. Right?
Right, bm_size is already equal to bdrv_nb_sectors(bs), and it's not
necessarily a multiple of dsc. So that should be good. Alternatively, I
think the following would be slightly easier to read:
assert(DIV_ROUND_UP(bm_size, dsc) == tb_size);
>
>>> +
>>> + bdrv_dirty_bitmap_serialize_part(bitmap, buf, sector, end -
>>> sector);
>>> + if (write_size < s->cluster_size) {
>>> + memset(buf + write_size, 0, s->cluster_size - write_size);
>>> + }
>> Should we assert that write_size <= s->cluster_size?
>
> Ok
>
> [...].
>
>>
>>> + const char *name = bdrv_dirty_bitmap_name(bitmap);
>>> + uint32_t granularity = bdrv_dirty_bitmap_granularity(bitmap);
>>> + Qcow2Bitmap *bm;
>>> +
>>> + if (!bdrv_dirty_bitmap_get_persistance(bitmap)) {
>>> + continue;
>>> + }
>>> +
>>> + if (++new_nb_bitmaps > QCOW2_MAX_BITMAPS) {
>>> + error_setg(errp, "Too many persistent bitmaps");
>>> + goto fail;
>>> + }
>>> +
>>> + new_dir_size += calc_dir_entry_size(strlen(name), 0);
>>> + if (new_dir_size > QCOW2_MAX_BITMAP_DIRECTORY_SIZE) {
>>> + error_setg(errp, "Too large bitmap directory");
>>> + goto fail;
>>> + }
>> You only need to increment new_nb_bitmaps and increase new_dir_size if
>> the bitmap does not already exist in the image (i.e. if
>> find_bitmap_by_name() below returns NULL).
>
> Why? No, I need to check the whole sum and the whole size.
If the bitmap already exists, you don't create a new directory entry but
reuse the existing one. Therefore, the number of bitmaps in the image
and the directory size will not grow then.
Max
>>> +
>>> + if (check_constraints_on_bitmap(bs, name, granularity) < 0) {
>>> + error_setg(errp, "Bitmap '%s' doesn't satisfy the constraints",
>>> + name);
>>> + goto fail;
>>> + }
>>> +
>>> + bm = find_bitmap_by_name(bm_list, name);
>>> + if (bm == NULL) {
>>> + bm = g_new0(Qcow2Bitmap, 1);
>>> + bm->name = g_strdup(name);
>>> + QSIMPLEQ_INSERT_TAIL(bm_list, bm, entry);
>>> + } else {
>>> + if (!(bm->flags & BME_FLAG_IN_USE) && can_write(bs)) {
>> Shouldn't we error out right at the beginning of this function if
>> can_write(bs) is false?
>
> Hmm, right.
>
> [...]
>
> --
> Best regards,
> Vladimir
>
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