[Qemu-devel] [PATCH 07/12] block: introduce bdrv_zeroize

[Peter Lieven]

this patch adds a call to completely zero out a block device.
the operation is speed up by checking the block status and
only writing zeroes to the device if they currently do not
return zeroes. optionally the zero writing can be speed up
by setting the flag BDRV_REQ_MAY_UNMAP to emulate the zero
write by unmapping if the driver supports it.

Signed-off-by: Peter Lieven <address@hidden>
---
 block.c               |   45 +++++++++++++++++++++++++++++++++++++++++++++
 include/block/block.h |    1 +
 2 files changed, 46 insertions(+)

diff --git a/block.c b/block.c
index 6f498fc..76a6621 100644
--- a/block.c
+++ b/block.c
@@ -2342,6 +2342,51 @@ int bdrv_write_zeroes(BlockDriverState *bs, int64_t 
sector_num,
                       BDRV_REQ_ZERO_WRITE | flags);
 }
 
+int bdrv_zeroize(BlockDriverState *bs, BdrvRequestFlags flags)
+{
+    BlockDriverInfo bdi;
+    int64_t target_size = bdrv_getlength(bs) / BDRV_SECTOR_SIZE;
+    int64_t ret, nb_sectors, sector_num = 0;
+    int n;
+    /* split the write requests into 1MB chunks if the driver
+     * does not return a maximal size via bdi */
+    int max_write_zeroes = 1 << (20 - BDRV_SECTOR_BITS);
+    if (bdrv_get_info(bs, &bdi) == 0 &&
+        bdi.max_write_zeroes > 0) {
+        max_write_zeroes = bdi.max_write_zeroes;
+    }
+    for (;;) {
+        nb_sectors = target_size - sector_num;
+        if (nb_sectors <= 0) {
+            return 0;
+        }
+        if (nb_sectors > INT_MAX) {
+            nb_sectors = INT_MAX;
+        }
+        ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &n);
+        if (ret & BDRV_BLOCK_ZERO) {
+            sector_num += n;
+            continue;
+        }
+        while (n > 0) {
+            nb_sectors = n;
+            if (nb_sectors > max_write_zeroes) {
+                nb_sectors = max_write_zeroes;
+            }
+            ret = bdrv_write_zeroes(bs, sector_num, nb_sectors,
+                                    flags & BDRV_REQ_MAY_UNMAP);
+            if (ret < 0) {
+                error_report("error writing zeroes at sector %" PRId64 ": %s",
+                             sector_num, strerror(-ret));
+                return -EIO;
+            }
+            sector_num += nb_sectors;
+            n -= nb_sectors;
+        }
+    }
+}
+
+
 int bdrv_pread(BlockDriverState *bs, int64_t offset,
                void *buf, int count1)
 {
diff --git a/include/block/block.h b/include/block/block.h
index ee17048..71e9fa1 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -198,6 +198,7 @@ int bdrv_write(BlockDriverState *bs, int64_t sector_num,
                const uint8_t *buf, int nb_sectors);
 int bdrv_write_zeroes(BlockDriverState *bs, int64_t sector_num,
                int nb_sectors, BdrvRequestFlags flags);
+int bdrv_zeroize(BlockDriverState *bs, BdrvRequestFlags flags);
 int bdrv_writev(BlockDriverState *bs, int64_t sector_num, QEMUIOVector *qiov);
 int bdrv_pread(BlockDriverState *bs, int64_t offset,
                void *buf, int count);
-- 
1.7.9.5