[Qemu-devel] [RFC][PATCH] qemu-img: add support for skipping zeroes in input during convert

[Peter Lieven <pl@kamp.de>]

Signed-off-by: Peter Lieven <pl@kamp.de>
---
 qemu-img.c |   52 ++++++++++++++++++++++++++++++----------------------
 1 file changed, 30 insertions(+), 22 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index b6b5644..808f8f8 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1121,8 +1121,9 @@ out3:
 
 static int img_convert(int argc, char **argv)
 {
-    int c, ret = 0, n, n1, bs_n, bs_i, compress, cluster_size,
+    int c, n, n1, bs_n, bs_i, compress, cluster_size,
         cluster_sectors, skip_create;
+    int64_t ret = 0;
     int progress = 0, flags;
     const char *fmt, *out_fmt, *cache, *out_baseimg, *out_filename;
     BlockDriver *drv, *proto_drv;
@@ -1479,11 +1480,6 @@ static int img_convert(int argc, char **argv)
             if (nb_sectors <= 0) {
                 break;
             }
-            if (nb_sectors >= (IO_BUF_SIZE / 512)) {
-                n = (IO_BUF_SIZE / 512);
-            } else {
-                n = nb_sectors;
-            }
 
             while (sector_num - bs_offset >= bs_sectors) {
                 bs_i ++;
@@ -1495,34 +1491,46 @@ static int img_convert(int argc, char **argv)
                    sector_num, bs_i, bs_offset, bs_sectors); */
             }
 
-            if (n > bs_offset + bs_sectors - sector_num) {
-                n = bs_offset + bs_sectors - sector_num;
-            }
-
-            /* If the output image is being created as a copy on write image,
-               assume that sectors which are unallocated in the input image
-               are present in both the output's and input's base images (no
-               need to copy them). */
-            if (out_baseimg) {
-                ret = bdrv_is_allocated(bs[bs_i], sector_num - bs_offset,
-                                        n, &n1);
+            if (out_baseimg || has_zero_init) {
+                n = nb_sectors > INT_MAX ? INT_MAX : nb_sectors;
+                ret = bdrv_get_block_status(bs[bs_i], sector_num - bs_offset,
+                                            n, &n1);
                 if (ret < 0) {
-                    error_report("error while reading metadata for sector "
-                                 "%" PRId64 ": %s",
+                    error_report("error while reading block status of sector %" PRId64 ": %s",
                                  sector_num - bs_offset, strerror(-ret));
                     goto out;
                 }
-                if (!ret) {
+                /* If the output image is zero initialized, we are not working
+                 * on a shared base and the input is zero we can skip the next
+                 * n1 bytes */
+                if (!out_baseimg && has_zero_init && ret & BDRV_BLOCK_ZERO) {
+                    sector_num += n1;
+                    continue;
+                }
+                /* If the output image is being created as a copy on write image,
+                   assume that sectors which are unallocated in the input image
+                   are present in both the output's and input's base images (no
+                   need to copy them). */
+                if (out_baseimg && !(ret & BDRV_BLOCK_DATA)) {
                     sector_num += n1;
                     continue;
                 }
                 /* The next 'n1' sectors are allocated in the input image. Copy
                    only those as they may be followed by unallocated sectors. */
-                n = n1;
+                nb_sectors = n1;
+            }
+
+            if (nb_sectors >= (IO_BUF_SIZE / 512)) {
+                n = (IO_BUF_SIZE / 512);
             } else {
-                n1 = n;
+                n = nb_sectors;
+            }
+
+            if (n > bs_offset + bs_sectors - sector_num) {
+                n = bs_offset + bs_sectors - sector_num;
             }
 
+            n1 = n;
             ret = bdrv_read(bs[bs_i], sector_num - bs_offset, buf, n);
             if (ret < 0) {
                 error_report("error while reading sector %" PRId64 ": %s",
-- 
1.7.9.5