[PATCH v6 4/5] qemu-img: Add convert --bitmaps option

[Eric Blake <eblake@redhat.com>]

Make it easier to copy all the persistent bitmaps of (the top layer
of) a source image along with its guest-visible contents, by adding a
boolean flag for use with qemu-img convert.  This is basically
shorthand, as the same effect could be accomplished with a series of
'qemu-img bitmap --add' and 'qemu-img bitmap --merge -b source'
commands, or by their corresponding QMP commands.

Note that this command will fail in the same scenarios where 'qemu-img
measure' omits a 'bitmaps size:' line, namely, when either the source
or the destination lacks persistent bitmap support altogether.

See also https://bugzilla.redhat.com/show_bug.cgi?id=1779893

While touching this, clean up a couple coding issues spotted in the
same function: an extra blank line, and merging back-to-back 'if
(!skip_create)' blocks.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 docs/tools/qemu-img.rst |  6 +++-
 qemu-img.c              | 78 +++++++++++++++++++++++++++++++++++++++--
 qemu-img-cmds.hx        |  4 +--
 3 files changed, 82 insertions(+), 6 deletions(-)

diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
index 320cb52b9f61..69cd9a30373a 100644
--- a/docs/tools/qemu-img.rst
+++ b/docs/tools/qemu-img.rst
@@ -162,6 +162,10 @@ Parameters to convert subcommand:

 .. program:: qemu-img-convert

+.. option:: --bitmaps
+
+  Additionally copy all persistent bitmaps from the top layer of the source
+
 .. option:: -n

   Skip the creation of the target volume
@@ -397,7 +401,7 @@ Command description:
   4
     Error on reading data

-.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [--target-is-zero] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME
+.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [--target-is-zero] [--bitmaps] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME

   Convert the disk image *FILENAME* or a snapshot *SNAPSHOT_PARAM*
   to disk image *OUTPUT_FILENAME* using format *OUTPUT_FMT*. It can
diff --git a/qemu-img.c b/qemu-img.c
index 0778d8f56614..8ecebe178890 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -78,6 +78,7 @@ enum {
     OPTION_ENABLE = 272,
     OPTION_DISABLE = 273,
     OPTION_MERGE = 274,
+    OPTION_BITMAPS = 275,
 };

 typedef enum OutputFormat {
@@ -191,6 +192,7 @@ static void QEMU_NORETURN help(void)
            "       hiding corruption that has already occurred.\n"
            "\n"
            "Parameters to convert subcommand:\n"
+           "  '--bitmaps' copies all top-level persistent bitmaps to destination\n"
            "  '-m' specifies how many coroutines work in parallel during the convert\n"
            "       process (defaults to 8)\n"
            "  '-W' allow to write to the target out of order rather than sequential\n"
@@ -2139,6 +2141,39 @@ static int convert_do_copy(ImgConvertState *s)
     return s->ret;
 }

+static int convert_copy_bitmaps(BlockDriverState *src, BlockDriverState *dst)
+{
+    BdrvDirtyBitmap *bm;
+    Error *err = NULL;
+
+    FOR_EACH_DIRTY_BITMAP(src, bm) {
+        const char *name;
+
+        if (!bdrv_dirty_bitmap_get_persistence(bm)) {
+            continue;
+        }
+        name = bdrv_dirty_bitmap_name(bm);
+        qmp_block_dirty_bitmap_add(dst->node_name, name,
+                                   true, bdrv_dirty_bitmap_granularity(bm),
+                                   true, true,
+                                   true, !bdrv_dirty_bitmap_enabled(bm),
+                                   &err);
+        if (err) {
+            error_reportf_err(err, "Failed to create bitmap %s: ", name);
+            return -1;
+        }
+
+        do_dirty_bitmap_merge(dst->node_name, name, src->node_name, name,
+                              &err);
+        if (err) {
+            error_reportf_err(err, "Failed to populate bitmap %s: ", name);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
 #define MAX_BUF_SECTORS 32768

 static int img_convert(int argc, char **argv)
@@ -2160,6 +2195,8 @@ static int img_convert(int argc, char **argv)
     int64_t ret = -EINVAL;
     bool force_share = false;
     bool explict_min_sparse = false;
+    bool bitmaps = false;
+    size_t nbitmaps = 0;

     ImgConvertState s = (ImgConvertState) {
         /* Need at least 4k of zeros for sparse detection */
@@ -2179,6 +2216,7 @@ static int img_convert(int argc, char **argv)
             {"target-image-opts", no_argument, 0, OPTION_TARGET_IMAGE_OPTS},
             {"salvage", no_argument, 0, OPTION_SALVAGE},
             {"target-is-zero", no_argument, 0, OPTION_TARGET_IS_ZERO},
+            {"bitmaps", no_argument, 0, OPTION_BITMAPS},
             {0, 0, 0, 0}
         };
         c = getopt_long(argc, argv, ":hf:O:B:Cco:l:S:pt:T:qnm:WU",
@@ -2304,6 +2342,9 @@ static int img_convert(int argc, char **argv)
              */
             s.has_zero_init = true;
             break;
+        case OPTION_BITMAPS:
+            bitmaps = true;
+            break;
         }
     }

@@ -2365,7 +2406,6 @@ static int img_convert(int argc, char **argv)
         goto fail_getopt;
     }

-
     /* ret is still -EINVAL until here */
     ret = bdrv_parse_cache_mode(src_cache, &src_flags, &src_writethrough);
     if (ret < 0) {
@@ -2525,6 +2565,27 @@ static int img_convert(int argc, char **argv)
         }
     }

+    /* Determine how many bitmaps need copying */
+    if (bitmaps) {
+        BdrvDirtyBitmap *bm;
+
+        if (s.src_num > 1) {
+            error_report("Copying bitmaps only possible with single source");
+            ret = -1;
+            goto out;
+        }
+        if (!bdrv_supports_persistent_dirty_bitmap(blk_bs(s.src[0]))) {
+            error_report("Source lacks bitmap support");
+            ret = -1;
+            goto out;
+        }
+        FOR_EACH_DIRTY_BITMAP(blk_bs(s.src[0]), bm) {
+            if (bdrv_dirty_bitmap_get_persistence(bm)) {
+                nbitmaps++;
+            }
+        }
+    }
+
     /*
      * The later open call will need any decryption secrets, and
      * bdrv_create() will purge "opts", so extract them now before
@@ -2533,9 +2594,7 @@ static int img_convert(int argc, char **argv)
     if (!skip_create) {
         open_opts = qdict_new();
         qemu_opt_foreach(opts, img_add_key_secrets, open_opts, &error_abort);
-    }

-    if (!skip_create) {
         /* Create the new image */
         ret = bdrv_create(drv, out_filename, opts, &local_err);
         if (ret < 0) {
@@ -2573,6 +2632,13 @@ static int img_convert(int argc, char **argv)
     }
     out_bs = blk_bs(s.target);

+    if (nbitmaps > 0 && !bdrv_supports_persistent_dirty_bitmap(out_bs)) {
+        error_report("Format driver '%s' does not support bitmaps",
+                     out_fmt);
+        ret = -1;
+        goto out;
+    }
+
     if (s.compressed && !block_driver_can_compress(out_bs->drv)) {
         error_report("Compression not supported for this file format");
         ret = -1;
@@ -2632,6 +2698,12 @@ static int img_convert(int argc, char **argv)
     }

     ret = convert_do_copy(&s);
+
+    /* Now copy the bitmaps */
+    if (nbitmaps > 0 && ret == 0) {
+        ret = convert_copy_bitmaps(blk_bs(s.src[0]), out_bs);
+    }
+
 out:
     if (!ret) {
         qemu_progress_print(100, 0);
diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index a87d3cb264ce..10b910b67cf8 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -46,9 +46,9 @@ SRST
 ERST

 DEF("convert", img_convert,
-    "convert [--object objectdef] [--image-opts] [--target-image-opts] [--target-is-zero] [-U] [-C] [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-B backing_file] [-o options] [-l snapshot_param] [-S sparse_size] [-m num_coroutines] [-W] [--salvage] filename [filename2 [...]] output_filename")
+    "convert [--object objectdef] [--image-opts] [--target-image-opts] [--target-is-zero] [--bitmaps] [-U] [-C] [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-B backing_file] [-o options] [-l snapshot_param] [-S sparse_size] [-m num_coroutines] [-W] [--salvage] filename [filename2 [...]] output_filename")
 SRST
-.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [--target-is-zero] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] [--salvage] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME
+.. option:: convert [--object OBJECTDEF] [--image-opts] [--target-image-opts] [--target-is-zero] [--bitmaps] [-U] [-C] [-c] [-p] [-q] [-n] [-f FMT] [-t CACHE] [-T SRC_CACHE] [-O OUTPUT_FMT] [-B BACKING_FILE] [-o OPTIONS] [-l SNAPSHOT_PARAM] [-S SPARSE_SIZE] [-m NUM_COROUTINES] [-W] [--salvage] FILENAME [FILENAME2 [...]] OUTPUT_FILENAME
 ERST

 DEF("create", img_create,
-- 
2.26.2