[Qemu-devel] [RESEND] [PATCH] Properly use backing file argument to git-img convert

[Brad Campbell]

 Converting to an image with an output backing file would write out the contents
 of the source image whether or not it was already contained in the new backing
 file. This commit ensures that the source file is checked against the new
 backing file and output is only allocated if it obsoletes or extends data
 already in the supplied backing file.


Signed-off-by: Brad Campbell <address@hidden>
---
 qemu-img.c |   74 ++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 files changed, 57 insertions(+), 17 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index c8a70ff..3fb6cbf 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -629,11 +629,12 @@ static int img_convert(int argc, char **argv)
     int progress = 0, flags;
     const char *fmt, *out_fmt, *cache, *out_baseimg, *out_filename;
     BlockDriver *drv, *proto_drv;
-    BlockDriverState **bs = NULL, *out_bs = NULL;
+    BlockDriverState **bs = NULL, *out_bs = NULL, *out_bf = NULL;
     int64_t total_sectors, nb_sectors, sector_num, bs_offset;
-    uint64_t bs_sectors;
+    uint64_t bf_sectors, bs_sectors;
     uint8_t * buf = NULL;
     const uint8_t *buf1;
+    uint8_t * bf_buf = NULL;
     BlockDriverInfo bdi;
     QEMUOptionParameter *param = NULL, *create_options = NULL;
     QEMUOptionParameter *out_baseimg_param;
@@ -797,6 +798,16 @@ static int img_convert(int argc, char **argv)
     out_baseimg_param = get_option_parameter(param, BLOCK_OPT_BACKING_FILE);
     if (out_baseimg_param) {
         out_baseimg = out_baseimg_param->value.s;
+
+        /* out_baseimg_parm != NULL even if there is no base img specified! */
+        if (out_baseimg) {
+            out_bf = bdrv_new_open(out_baseimg, NULL, BDRV_O_FLAGS);
+            if (!out_bf) {
+                ret = -1;
+                goto out;
+            }
+            bdrv_get_geometry(out_bf, &bf_sectors);
+        }
     }
 
     /* Check if compression is supported */
@@ -862,6 +873,9 @@ static int img_convert(int argc, char **argv)
     bs_offset = 0;
     bdrv_get_geometry(bs[0], &bs_sectors);
     buf = qemu_blockalign(out_bs, IO_BUF_SIZE);
+    if (out_baseimg) {
+        bf_buf = qemu_blockalign(out_bs, IO_BUF_SIZE);
+    }
 
     if (compress) {
         ret = bdrv_get_info(out_bs, &bdi);
@@ -979,31 +993,52 @@ static int img_convert(int argc, char **argv)
                 n = bs_offset + bs_sectors - sector_num;
             }
 
+            ret = bdrv_read(bs[bs_i], sector_num - bs_offset, buf, n);
+            if (ret < 0) {
+                error_report("error while reading sector %" PRId64 ": %s",
+                             sector_num - bs_offset, strerror(-ret));
+                goto out;
+            }
+        
             if (has_zero_init) {
                 /* 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). */
+                   check that sectors which are unallocated in the input image
+                   are present in both the output's and input's base images 
(or 
+                   copy them). */
                 if (out_baseimg) {
-                    if (!bdrv_is_allocated(bs[bs_i], sector_num - bs_offset,
-                                           n, &n1)) {
-                        sector_num += n1;
-                        continue;
+                    if (sector_num < bf_sectors) {
+                        /* Check if source sectors match those in the new 
backing file and
+                           skip the copy if true. */
+                        n = MIN(n, bf_sectors - sector_num);
+                        ret = bdrv_read(out_bf, sector_num - bs_offset, 
bf_buf, n);
+                        if (ret < 0) {
+                            error_report("error while reading backing file");
+                            goto out;
+                        }
+                        if (!compare_sectors(buf, bf_buf, n, &n1)) {
+                            sector_num += n1;
+                            continue;
+                        }
+ 
+                    } else {
+                        /* Source file(s) is larger than the backing file. 
Just check for
+                           allocated sectors */
+                        if (!is_allocated_sectors_min(buf, n, &n1, 
min_sparse)) {
+                            /* if we got zero, how many of the next ones are 
zero? */
+                            is_allocated_sectors(buf, n, &n1);
+                            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. */
+                    /* The next 'n1' sectors are allocated in the input image 
or the
+                       backing files are different. Copy only those as they 
may be 
+                       followed by unallocated sectors. */
                     n = n1;
                 }
             } else {
                 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",
-                             sector_num - bs_offset, strerror(-ret));
-                goto out;
-            }
             /* NOTE: at the same time we convert, we do not write zero
                sectors to have a chance to compress the image. Ideally, we
                should add a specific call to have the info to go faster */
@@ -1037,6 +1072,7 @@ out:
     free_option_parameters(create_options);
     free_option_parameters(param);
     qemu_vfree(buf);
+    qemu_vfree(bf_buf);
     if (out_bs) {
         bdrv_delete(out_bs);
     }
@@ -1048,6 +1084,10 @@ out:
         }
         g_free(bs);
     }
+    if (out_bf) {
+        bdrv_delete(out_bf);
+    }
+
     if (ret) {
         return 1;
     }
-- 
1.7.2.5