[Qemu-devel] [RFC V3 03/24] qcow2: Add qcow2_dedup_read_missing_and_concatenate

["Benoît Canet" <benoit@irqsave.net>]

This function is used to read missing data when unaligned writes are
done. This function also concatenate missing data with the given
qiov data in order to prepare a buffer used to look for duplicated
clusters.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
---
 block/Makefile.objs |    1 +
 block/qcow2-dedup.c |  150 +++++++++++++++++++++++++++++++++++++++++++++++++++
 block/qcow2.h       |    8 +++
 3 files changed, 159 insertions(+)
 create mode 100644 block/qcow2-dedup.c

diff --git a/block/Makefile.objs b/block/Makefile.objs
index 554f429..790cb5f 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -1,5 +1,6 @@
 block-obj-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat.o
 block-obj-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o qcow2-cache.o
+block-obj-y += qcow2-dedup.o
 block-obj-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o qed-cluster.o
 block-obj-y += qed-check.o
 block-obj-y += parallels.o nbd.o blkdebug.o sheepdog.o blkverify.o
diff --git a/block/qcow2-dedup.c b/block/qcow2-dedup.c
new file mode 100644
index 0000000..e4e6108
--- /dev/null
+++ b/block/qcow2-dedup.c
@@ -0,0 +1,150 @@
+/*
+ * Deduplication for the QCOW2 format
+ *
+ * Copyright (C) Nodalink, SARL. 2012
+ *
+ * Author:
+ *   Benoît Canet <benoit.canet@irqsave.net>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "block_int.h"
+#include "qemu-common.h"
+#include "qcow2.h"
+
+/**
+ * Read some data from the QCOW2 file
+ *
+ * @data:       the buffer where the data must be stored
+ * @sector_num: the sector number to read in the QCOW2 file
+ * @nb_sectors: the number of sectors to read
+ * @ret:        negative on error
+ */
+static int qcow2_dedup_read_missing_cluster_data(BlockDriverState *bs,
+                                                 uint8_t *data,
+                                                 uint64_t sector_num,
+                                                 int nb_sectors)
+{
+    BDRVQcowState *s = bs->opaque;
+    QEMUIOVector qiov;
+    struct iovec iov;
+    int ret;
+
+    iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE;
+    iov.iov_base = data;
+    qemu_iovec_init_external(&qiov, &iov, 1);
+    qemu_co_mutex_unlock(&s->lock);
+    ret = bdrv_co_readv(bs, sector_num, nb_sectors, &qiov);
+    qemu_co_mutex_lock(&s->lock);
+    if (ret < 0) {
+        error_report("failed to read %d sectors at offset %" PRIu64 "\n",
+                     nb_sectors, sector_num);
+    }
+
+    return ret;
+}
+
+/*
+ * Prepare a buffer containing all the required data required to compute cluster
+ * sized deduplication hashes.
+ * If sector_num and nb_sectors are unaligned cluster wize it read the missing
+ * data before and after the qiov.
+ *
+ * @qiov:               the qiov for which missing data must be read
+ * @sector_num:         the first sectors that must be read into the qiov
+ * @nb_sectors:         the number of sectors to read into the qiov
+ * @data:               the place where the data will be concatenated and stored
+ * @nb_data_sectors:    the resulting size of the contatenated data (in sectors)
+ * @ret:                negative on error
+ */
+int qcow2_dedup_read_missing_and_concatenate(BlockDriverState *bs,
+                                             QEMUIOVector *qiov,
+                                             uint64_t sector_num,
+                                             int nb_sectors,
+                                             uint8_t **data,
+                                             int *nb_data_sectors)
+{
+    BDRVQcowState *s = bs->opaque;
+    int ret;
+    uint64_t cluster_beginning_sector;
+    uint64_t first_sector_after_qiov;
+    int cluster_beginning_nr;
+    int cluster_ending_nr;
+    int unaligned_ending_nr;
+    uint64_t max_cluster_ending_nr;
+
+    /* compute how much and where to read at the beginning */
+    cluster_beginning_nr = sector_num & (s->cluster_sectors - 1);
+    cluster_beginning_sector = sector_num - cluster_beginning_nr;
+
+    /* for the ending */
+    first_sector_after_qiov = sector_num + nb_sectors;
+    unaligned_ending_nr = first_sector_after_qiov & (s->cluster_sectors - 1);
+    cluster_ending_nr = unaligned_ending_nr ?
+                        s->cluster_sectors - unaligned_ending_nr : 0;
+
+    /* compute total size in sectors and allocate memory */
+    *nb_data_sectors = cluster_beginning_nr + nb_sectors + cluster_ending_nr;
+    *data = qemu_blockalign(bs, *nb_data_sectors * BDRV_SECTOR_SIZE);
+    memset(*data, 0, *nb_data_sectors * BDRV_SECTOR_SIZE);
+
+    /* read beginning */
+    if (cluster_beginning_nr) {
+        ret = qcow2_dedup_read_missing_cluster_data(bs,
+                                                    *data,
+                                                    cluster_beginning_sector,
+                                                    cluster_beginning_nr);
+
+        if (ret < 0) {
+            goto fail;
+        }
+    }
+
+    /* append qiov content */
+    qemu_iovec_to_buf(qiov, 0, *data + cluster_beginning_nr * BDRV_SECTOR_SIZE,
+                      qiov->size);
+
+    /* Fix cluster_ending_nr if we are at risk of reading outside the image
+     * (Cluster unaligned image size)
+     */
+    max_cluster_ending_nr = bs->total_sectors - first_sector_after_qiov;
+    cluster_ending_nr = max_cluster_ending_nr < (uint64_t) cluster_ending_nr ?
+                        (int) max_cluster_ending_nr : cluster_ending_nr;
+
+    /* read and add ending */
+    if (cluster_ending_nr) {
+        ret = qcow2_dedup_read_missing_cluster_data(bs,
+                                                    *data +
+                                                    (cluster_beginning_nr +
+                                                    nb_sectors) *
+                                                    BDRV_SECTOR_SIZE,
+                                                    first_sector_after_qiov,
+                                                    cluster_ending_nr);
+
+        if (ret < 0) {
+            goto fail;
+        }
+    }
+
+    return 0;
+
+fail:
+    return ret;
+}
diff --git a/block/qcow2.h b/block/qcow2.h
index e192001..858fef3 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -359,4 +359,12 @@ int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset,
     void **table);
 int qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table);
 
+/* qcow2-dedup.c functions */
+int qcow2_dedup_read_missing_and_concatenate(BlockDriverState *bs,
+                                             QEMUIOVector *qiov,
+                                             uint64_t sector,
+                                             int sectors_nr,
+                                             uint8_t **dedup_cluster_data,
+                                             int *dedup_cluster_data_nr);
+
 #endif
-- 
1.7.10.4