[PATCH v3 0/4] qemu-img compare --stat

[PATCH v3 0/4] qemu-img compare --stat

[Vladimir Sementsov-Ogievskiy]

Hi all!

Recently we faced the following task:

Customer comes and say: incremental backup images are too fat. Does you
incremental backup works correct?

What to answer? We should check something. At least check that
incremental images doesn't store same data twice. And we don't have a
tool for it. I just wrote a simple python script to compare raw files
cluster-by-cluster. Then we've mounted the qcow2 images with help of
qemu-nbd, the resulting /dev/nbd* were compared and we proved that
incremental backups don't store same data.

But that leads to idea that some kind of that script would be good to
have at hand.

So, here is a new option for qemu-img compare, that is a lot more
powerful and effective than original script, and allows to compare and
calculate statistics, i.e. how many clusters differs, how many
clusters changed from unallocated to data, and so on.

For examples of output look at the test in patch 04.

v3:
qemu-img: implement compare --stat
  fix wording
  fix option numbers
  allocate ImgCmpStat dynamically
  fix exit statuses
  restrict using strict mode together with --stat

qemu-img: make --block-size optional for compare --stat
  fix wording

qemu-img: add --shallow option for qemu-img compare
  fix option number(rebase on previous fix)
  add Hanna's r-b

iotests: add qemu-img-compare-stat test
  add Hanna's r-b
  s/Agenda/Key/ in test output

Vladimir Sementsov-Ogievskiy (4):
  qemu-img: implement compare --stat
  qemu-img: make --block-size optional for compare --stat
  qemu-img: add --shallow option for qemu-img compare
  iotests: add qemu-img-compare-stat test

 docs/tools/qemu-img.rst                       |  30 +-
 qemu-img.c                                    | 275 +++++++++++++++++-
 qemu-img-cmds.hx                              |   4 +-
 .../qemu-iotests/tests/qemu-img-compare-stat  |  88 ++++++
 .../tests/qemu-img-compare-stat.out           | 106 +++++++
 5 files changed, 485 insertions(+), 18 deletions(-)
 create mode 100755 tests/qemu-iotests/tests/qemu-img-compare-stat
 create mode 100644 tests/qemu-iotests/tests/qemu-img-compare-stat.out

-- 
2.31.1

[PATCH v3 1/4] qemu-img: implement compare --stat

[Vladimir Sementsov-Ogievskiy]

With new option qemu-img compare will not stop at first mismatch, but
instead calculate statistics: how many clusters with different data,
how many clusters with equal data, how many clusters were unallocated
but become data and so on.

We compare images chunk by chunk. Chunk size depends on what
block_status returns for both images. It may return less than cluster
(remember about qcow2 subclusters), it may return more than cluster (if
several consecutive clusters share same status). Finally images may
have different cluster sizes. This all leads to ambiguity in how to
finally compare the data.

What we can say for sure is that, when we compare two qcow2 images with
same cluster size, we should compare clusters with data separately.
Otherwise, if we for example compare 10 consecutive clusters of data
where only one byte differs we'll report 10 different clusters.
Expected result in this case is 1 different cluster and 9 equal ones.

So, to serve this case and just to have some defined rule let's do the
following:

1. Select some block-size for compare procedure. In this commit it must
   be specified by user, next commit will add some automatic logic and
   make --block-size optional.

2. Go chunk-by-chunk using block_status as we do now with only one
   differency:
   If block_status() returns DATA region that intersects block-size
   aligned boundary, crop this region at this boundary.

This way it's still possible to compare less than cluster and report
subcluster-level accuracy, but we newer compare more than one cluster
of data.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 docs/tools/qemu-img.rst |  18 +++-
 qemu-img.c              | 210 +++++++++++++++++++++++++++++++++++++---
 qemu-img-cmds.hx        |   4 +-
 3 files changed, 216 insertions(+), 16 deletions(-)

diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
index d58980aef8..8b6b799dd4 100644
--- a/docs/tools/qemu-img.rst
+++ b/docs/tools/qemu-img.rst
@@ -159,6 +159,18 @@ Parameters to compare subcommand:
 
   Strict mode - fail on different image size or sector allocation
 
+.. option:: --stat
+
+  Instead of exiting on the first mismatch, compare the whole images
+  and print statistics on the amount of different pairs of blocks,
+  based on their block status and whether they are equal or not.
+
+.. option:: --block-size BLOCK_SIZE
+
+  Block size for comparing with ``--stat``. This doesn't guarantee an
+  exact size for comparing chunks, but it does guarantee that those
+  chunks will never cross a block-size-aligned boundary.
+
 Parameters to convert subcommand:
 
 .. program:: qemu-img-convert
@@ -378,7 +390,7 @@ Command description:
 
   The rate limit for the commit process is specified by ``-r``.
 
-.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] FILENAME1 FILENAME2
+.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat --block-size BLOCK_SIZE] FILENAME1 FILENAME2
 
   Check if two images have the same content. You can compare images with
   different format or settings.
@@ -405,9 +417,9 @@ Command description:
   The following table sumarizes all exit codes of the compare subcommand:
 
   0
-    Images are identical (or requested help was printed)
+    Images are identical (or requested help was printed, or ``--stat`` was used)
   1
-    Images differ
+    Images differ (1 is never returned when ``--stat`` option specified)
   2
     Error on opening an image
   3
diff --git a/qemu-img.c b/qemu-img.c
index f036a1d428..0cb7cebe91 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -83,6 +83,8 @@ enum {
     OPTION_BITMAPS = 275,
     OPTION_FORCE = 276,
     OPTION_SKIP_BROKEN = 277,
+    OPTION_STAT = 278,
+    OPTION_BLOCK_SIZE = 279,
 };
 
 typedef enum OutputFormat {
@@ -1304,6 +1306,107 @@ static int check_empty_sectors(BlockBackend *blk, int64_t offset,
     return 0;
 }
 
+#define IMG_CMP_STATUS_MASK (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO | \
+                             BDRV_BLOCK_ALLOCATED)
+#define IMG_CMP_STATUS_MAX (IMG_CMP_STATUS_MASK | BDRV_BLOCK_EOF)
+
+typedef struct ImgCmpStat {
+    /* stat: [ret: 0 is equal, 1 is not][status1][status2] -> n_bytes */
+    uint64_t stat[2][IMG_CMP_STATUS_MAX + 1][IMG_CMP_STATUS_MAX + 1];
+} ImgCmpStat;
+
+/*
+ * To denote chunks after EOF when compared files are of different size, use
+ * corresponding status = -1
+ */
+static void cmp_stat_account(ImgCmpStat *stat, bool differs,
+                             int status1, int status2, int64_t bytes)
+{
+    assert(status1 >= -1);
+    if (status1 == -1) {
+        /*
+         * Note BDRV_BLOCK_EOF: we abuse it here a bit. User is not interested
+         * in EOF flag in the last chunk of file (especially when we trim the
+         * chunk and EOF becomes incorrect), so BDRV_BLOCK_EOF is not in
+         * IMG_CMP_STATUS_MASK. We instead use BDRV_BLOCK_EOF to illustrate
+         * chunks after-end-of-file in shorter file.
+         */
+        status1 = BDRV_BLOCK_EOF | BDRV_BLOCK_ZERO;
+    } else {
+        status1 &= IMG_CMP_STATUS_MASK;
+    }
+
+    assert(status2 >= -1);
+    if (status2 == -1) {
+        status2 = BDRV_BLOCK_EOF | BDRV_BLOCK_ZERO;
+    } else {
+        status2 &= IMG_CMP_STATUS_MASK;
+    }
+
+    stat->stat[differs][status1][status2] += bytes;
+}
+
+static void cmp_stat_print_agenda(void)
+{
+    printf("Compare stats:\n"
+           "Key\n"
+           "D: DATA\n"
+           "Z: ZERO\n"
+           "A: ALLOCATED\n"
+           "E: after end of file\n\n");
+}
+
+static void cmp_stat_print_status(int status)
+{
+    printf("%s%s%s%s",
+           status & BDRV_BLOCK_DATA ? "D" : "_",
+           status & BDRV_BLOCK_ZERO ? "Z" : "_",
+           status & BDRV_BLOCK_ALLOCATED ? "A" : "_",
+           status & BDRV_BLOCK_EOF ? "E" : "_");
+}
+
+static void cmp_stat_print(ImgCmpStat *stat, int64_t total_bytes)
+{
+    int ret, status1, status2;
+
+    cmp_stat_print_agenda();
+
+    for (ret = 0; ret <= 1; ret++) {
+        uint64_t total_in_group = 0;
+
+        if (ret == 0) {
+            printf("Equal:\n");
+        } else {
+            printf("\nUnequal:\n");
+        }
+
+        for (status1 = 0; status1 <= IMG_CMP_STATUS_MAX; status1++) {
+            for (status2 = 0; status2 <= IMG_CMP_STATUS_MAX; status2++) {
+                uint64_t bytes = stat->stat[ret][status1][status2];
+                g_autofree char *bytes_str = NULL;
+
+                if (!bytes) {
+                    continue;
+                }
+
+                total_in_group += bytes;
+
+                cmp_stat_print_status(status1);
+                printf(" -> ");
+                cmp_stat_print_status(status2);
+
+                bytes_str = size_to_str(bytes);
+                printf(" %" PRIu64 " bytes (%s) %.1f%%\n", bytes, bytes_str,
+                       100.0 * bytes / total_bytes);
+            }
+        }
+
+        if (!total_in_group) {
+            printf("<nothing>\n");
+        }
+    }
+}
+
 /*
  * Compares two images. Exit codes:
  *
@@ -1320,6 +1423,8 @@ static int img_compare(int argc, char **argv)
     uint8_t *buf1 = NULL, *buf2 = NULL;
     int64_t pnum1, pnum2;
     int allocated1, allocated2;
+    int status1, status2;
+    int64_t block_end;
     int ret = 0; /* return value - 0 Ident, 1 Different, >1 Error */
     bool progress = false, quiet = false, strict = false;
     int flags;
@@ -1331,6 +1436,8 @@ static int img_compare(int argc, char **argv)
     uint64_t progress_base;
     bool image_opts = false;
     bool force_share = false;
+    g_autofree ImgCmpStat *stat = NULL;
+    int64_t block_size = 0;
 
     cache = BDRV_DEFAULT_CACHE;
     for (;;) {
@@ -1339,6 +1446,8 @@ static int img_compare(int argc, char **argv)
             {"object", required_argument, 0, OPTION_OBJECT},
             {"image-opts", no_argument, 0, OPTION_IMAGE_OPTS},
             {"force-share", no_argument, 0, 'U'},
+            {"stat", no_argument, 0, OPTION_STAT},
+            {"block-size", required_argument, 0, OPTION_BLOCK_SIZE},
             {0, 0, 0, 0}
         };
         c = getopt_long(argc, argv, ":hf:F:T:pqsU",
@@ -1395,6 +1504,15 @@ static int img_compare(int argc, char **argv)
         case OPTION_IMAGE_OPTS:
             image_opts = true;
             break;
+        case OPTION_STAT:
+            stat = g_new0(ImgCmpStat, 1);
+            break;
+        case OPTION_BLOCK_SIZE:
+            block_size = cvtnum_full("block size", optarg, 1, INT64_MAX);
+            if (block_size < 0) {
+                exit(2);
+            }
+            break;
         }
     }
 
@@ -1410,6 +1528,25 @@ static int img_compare(int argc, char **argv)
     filename1 = argv[optind++];
     filename2 = argv[optind++];
 
+    if (!stat && block_size) {
+        error_report("--block-size can be used only together with --stat");
+        ret = 2;
+        goto out3;
+    }
+
+    if (stat && !block_size) {
+        /* TODO: make block-size optional */
+        error_report("You must specify --block-size together with --stat");
+        ret = 2;
+        goto out3;
+    }
+
+    if (stat && strict) {
+        error_report("--stat can't be used together with -s");
+        ret = 2;
+        goto out3;
+    }
+
     /* Initialize before goto out */
     qemu_progress_init(progress, 2.0);
 
@@ -1465,7 +1602,7 @@ static int img_compare(int argc, char **argv)
     }
 
     while (offset < total_size) {
-        int status1, status2;
+        block_end = QEMU_ALIGN_UP(offset + 1, block_size);
 
         status1 = bdrv_block_status_above(bs1, NULL, offset,
                                           total_size1 - offset, &pnum1, NULL,
@@ -1476,6 +1613,10 @@ static int img_compare(int argc, char **argv)
             goto out;
         }
         allocated1 = status1 & BDRV_BLOCK_ALLOCATED;
+        if (stat && (status1 & BDRV_BLOCK_DATA)) {
+            /* Don't compare cross-block data */
+            pnum1 = MIN(block_end, offset + pnum1) - offset;
+        }
 
         status2 = bdrv_block_status_above(bs2, NULL, offset,
                                           total_size2 - offset, &pnum2, NULL,
@@ -1486,11 +1627,15 @@ static int img_compare(int argc, char **argv)
             goto out;
         }
         allocated2 = status2 & BDRV_BLOCK_ALLOCATED;
+        if (stat && (status2 & BDRV_BLOCK_DATA)) {
+            /* Don't compare cross-block data */
+            pnum2 = MIN(block_end, offset + pnum2) - offset;
+        }
 
         assert(pnum1 && pnum2);
         chunk = MIN(pnum1, pnum2);
 
-        if (strict) {
+        if (strict && !stat) {
             if (status1 != status2) {
                 ret = 1;
                 qprintf(quiet, "Strict mode: Offset %" PRId64
@@ -1499,7 +1644,8 @@ static int img_compare(int argc, char **argv)
             }
         }
         if ((status1 & BDRV_BLOCK_ZERO) && (status2 & BDRV_BLOCK_ZERO)) {
-            /* nothing to do */
+            /* nothing to do, equal: */
+            ret = 0;
         } else if (allocated1 == allocated2) {
             if (allocated1) {
                 int64_t pnum;
@@ -1523,25 +1669,37 @@ static int img_compare(int argc, char **argv)
                 }
                 ret = compare_buffers(buf1, buf2, chunk, &pnum);
                 if (ret || pnum != chunk) {
-                    qprintf(quiet, "Content mismatch at offset %" PRId64 "!\n",
+                    qprintf(quiet || stat,
+                            "Content mismatch at offset %" PRId64 "!\n",
                             offset + (ret ? 0 : pnum));
                     ret = 1;
-                    goto out;
                 }
+            } else {
+                /* Consider unallocated areas equal. */
+                ret = 0;
             }
         } else {
             chunk = MIN(chunk, IO_BUF_SIZE);
             if (allocated1) {
                 ret = check_empty_sectors(blk1, offset, chunk,
-                                          filename1, buf1, quiet);
+                                          filename1, buf1, quiet || stat);
             } else {
                 ret = check_empty_sectors(blk2, offset, chunk,
-                                          filename2, buf1, quiet);
+                                          filename2, buf1, quiet || stat);
             }
-            if (ret) {
+            assert(ret == 0 || ret == 1 || ret == 4);
+            if (ret == 4) {
                 goto out;
             }
         }
+        assert(ret == 0 || ret == 1);
+
+        if (stat) {
+            cmp_stat_account(stat, ret, status1, status2, chunk);
+        } else if (ret) {
+            goto out;
+        }
+
         offset += chunk;
         qemu_progress_print(((float) chunk / progress_base) * 100, 100);
     }
@@ -1549,17 +1707,24 @@ static int img_compare(int argc, char **argv)
     if (total_size1 != total_size2) {
         BlockBackend *blk_over;
         const char *filename_over;
+        int *status_over;
 
         qprintf(quiet, "Warning: Image size mismatch!\n");
         if (total_size1 > total_size2) {
             blk_over = blk1;
             filename_over = filename1;
+            status_over = &status1;
+            status2 = -1; /* Denote after-EOF for cmp_stat_account() */
         } else {
             blk_over = blk2;
             filename_over = filename2;
+            status1 = -1; /* Denote after-EOF for cmp_stat_account() */
+            status_over = &status2;
         }
 
         while (offset < progress_base) {
+            block_end = QEMU_ALIGN_UP(offset + 1, block_size);
+
             ret = bdrv_block_status_above(blk_bs(blk_over), NULL, offset,
                                           progress_base - offset, &chunk,
                                           NULL, NULL);
@@ -1570,20 +1735,43 @@ static int img_compare(int argc, char **argv)
                 goto out;
 
             }
+            if (stat && (ret & BDRV_BLOCK_DATA)) {
+                /* Don't compare cross-block data */
+                chunk = MIN(block_end, offset + chunk) - offset;
+            }
+            *status_over = ret;
+
             if (ret & BDRV_BLOCK_ALLOCATED && !(ret & BDRV_BLOCK_ZERO)) {
                 chunk = MIN(chunk, IO_BUF_SIZE);
                 ret = check_empty_sectors(blk_over, offset, chunk,
-                                          filename_over, buf1, quiet);
-                if (ret) {
+                                          filename_over, buf1,
+                                          quiet || stat);
+                assert(ret == 0 || ret == 1 || ret == 4);
+                if (ret == 4) {
                     goto out;
                 }
+            } else {
+                ret = 0;
             }
+            assert(ret == 0 || ret == 1);
+
+            if (stat) {
+                cmp_stat_account(stat, ret, status1, status2, chunk);
+            } else if (ret) {
+                goto out;
+            }
+
             offset += chunk;
             qemu_progress_print(((float) chunk / progress_base) * 100, 100);
         }
     }
 
-    qprintf(quiet, "Images are identical.\n");
+    if (stat) {
+        cmp_stat_print(stat, progress_base);
+    } else {
+        qprintf(quiet, "Images are identical.\n");
+    }
+
     ret = 0;
 
 out:
diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index 4c4d94ab22..0b2d63ca5f 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -40,9 +40,9 @@ SRST
 ERST
 
 DEF("compare", img_compare,
-    "compare [--object objectdef] [--image-opts] [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] [-U] filename1 filename2")
+    "compare [--object objectdef] [--image-opts] [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] [-U] [--stat --block-size BLOCK_SIZE] filename1 filename2")
 SRST
-.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] FILENAME1 FILENAME2
+.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat --block-size BLOCK_SIZE] FILENAME1 FILENAME2
 ERST
 
 DEF("convert", img_convert,
-- 
2.31.1

[PATCH v3 2/4] qemu-img: make --block-size optional for compare --stat

[Vladimir Sementsov-Ogievskiy]

Let's detect block-size automatically if not specified by user:

 If both files define cluster-size, use minimum to be more precise.
 If both files don't specify cluster-size, use default of 64K
 If only one file specify cluster-size, just use it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 docs/tools/qemu-img.rst |  7 +++-
 qemu-img.c              | 71 +++++++++++++++++++++++++++++++++++++----
 qemu-img-cmds.hx        |  4 +--
 3 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
index 8b6b799dd4..9bfdd93d6c 100644
--- a/docs/tools/qemu-img.rst
+++ b/docs/tools/qemu-img.rst
@@ -170,6 +170,11 @@ Parameters to compare subcommand:
   Block size for comparing with ``--stat``. This doesn't guarantee an
   exact size for comparing chunks, but it does guarantee that those
   chunks will never cross a block-size-aligned boundary.
+  When unspecified the following logic is used:
+
+    - If both files define cluster-size, use minimum to be more precise.
+    - If both files don't specify cluster-size, use default of 64K
+    - If only one file specifies cluster-size, just use that.
 
 Parameters to convert subcommand:
 
@@ -390,7 +395,7 @@ Command description:
 
   The rate limit for the commit process is specified by ``-r``.
 
-.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat --block-size BLOCK_SIZE] FILENAME1 FILENAME2
+.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat [--block-size BLOCK_SIZE]] FILENAME1 FILENAME2
 
   Check if two images have the same content. You can compare images with
   different format or settings.
diff --git a/qemu-img.c b/qemu-img.c
index 0cb7cebe91..905150671f 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1407,6 +1407,62 @@ static void cmp_stat_print(ImgCmpStat *stat, int64_t total_bytes)
     }
 }
 
+/* Get default value for qemu-img compare --block-size option. */
+static int img_compare_block_size(BlockDriverState *bs1,
+                                  BlockDriverState *bs2,
+                                  bool quiet)
+{
+    const int default_block_size = 64 * 1024; /* 64K */
+
+    int ret;
+    BlockDriverInfo bdi;
+    int cluster_size1, cluster_size2, block_size;
+    const char *note = "Note: to alter it, set --block-size option.";
+    const char *fname1 = bs1->filename;
+    const char *fname2 = bs2->filename;
+
+    ret = bdrv_get_info(bs1, &bdi);
+    if (ret < 0 && ret != -ENOTSUP) {
+        error_report("Failed to get info of %s: %s", fname1, strerror(-ret));
+        return ret;
+    }
+    cluster_size1 = ret < 0 ? 0 : bdi.cluster_size;
+
+    ret = bdrv_get_info(bs2, &bdi);
+    if (ret < 0 && ret != -ENOTSUP) {
+        error_report("Failed to get info of %s: %s", fname2, strerror(-ret));
+        return ret;
+    }
+    cluster_size2 = ret < 0 ? 0 : bdi.cluster_size;
+
+    if (cluster_size1 > 0 && cluster_size2 > 0) {
+        if (cluster_size1 == cluster_size2) {
+            block_size = cluster_size1;
+        } else {
+            block_size = MIN(cluster_size1, cluster_size2);
+            qprintf(quiet, "%s and %s have different cluster sizes: %d and %d "
+                    "respectively. Using minimum as block-size for "
+                    "accuracy: %d. %s\n",
+                    fname1, fname2, cluster_size1,
+                    cluster_size2, block_size, note);
+        }
+    } else if (cluster_size1 == 0 && cluster_size2 == 0) {
+        block_size = default_block_size;
+        qprintf(quiet, "Neither of %s and %s have an explicit cluster size. "
+                "Using default of %d bytes. %s\n", fname1, fname2, block_size,
+                note);
+    } else {
+        block_size = MAX(cluster_size1, cluster_size2);
+        qprintf(quiet, "%s has an explicit cluster size of %d and %s "
+                "doesn't have one. Using %d as block-size. %s\n",
+                cluster_size1 ? fname1 : fname2, block_size,
+                cluster_size1 ? fname2 : fname1,
+                block_size, note);
+    }
+
+    return block_size;
+}
+
 /*
  * Compares two images. Exit codes:
  *
@@ -1534,13 +1590,6 @@ static int img_compare(int argc, char **argv)
         goto out3;
     }
 
-    if (stat && !block_size) {
-        /* TODO: make block-size optional */
-        error_report("You must specify --block-size together with --stat");
-        ret = 2;
-        goto out3;
-    }
-
     if (stat && strict) {
         error_report("--stat can't be used together with -s");
         ret = 2;
@@ -1593,6 +1642,14 @@ static int img_compare(int argc, char **argv)
     total_size = MIN(total_size1, total_size2);
     progress_base = MAX(total_size1, total_size2);
 
+    if (stat && !block_size) {
+        block_size = img_compare_block_size(bs1, bs2, quiet);
+        if (block_size <= 0) {
+            ret = 4;
+            goto out;
+        }
+    }
+
     qemu_progress_print(0, 100);
 
     if (strict && total_size1 != total_size2) {
diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index 0b2d63ca5f..96a193eea8 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -40,9 +40,9 @@ SRST
 ERST
 
 DEF("compare", img_compare,
-    "compare [--object objectdef] [--image-opts] [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] [-U] [--stat --block-size BLOCK_SIZE] filename1 filename2")
+    "compare [--object objectdef] [--image-opts] [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] [-U] [--stat [--block-size BLOCK_SIZE]] filename1 filename2")
 SRST
-.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat --block-size BLOCK_SIZE] FILENAME1 FILENAME2
+.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat [--block-size BLOCK_SIZE]] FILENAME1 FILENAME2
 ERST
 
 DEF("convert", img_convert,
-- 
2.31.1

[PATCH v3 3/4] qemu-img: add --shallow option for qemu-img compare

[Vladimir Sementsov-Ogievskiy]

Allow compare only top images of backing chains. This is useful to
compare images with same backing file or to compare incremental images
from the chain of incremental backups with "--stat" option.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
---
 docs/tools/qemu-img.rst | 9 ++++++++-
 qemu-img.c              | 8 ++++++--
 qemu-img-cmds.hx        | 4 ++--
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
index 9bfdd93d6c..c6e9306c70 100644
--- a/docs/tools/qemu-img.rst
+++ b/docs/tools/qemu-img.rst
@@ -176,6 +176,13 @@ Parameters to compare subcommand:
     - If both files don't specify cluster-size, use default of 64K
     - If only one file specifies cluster-size, just use that.
 
+.. option:: --shallow
+
+  This option prevents opening and comparing any backing files.
+  This is useful to compare images with same backing file or to compare
+  incremental images from the chain of incremental backups with
+  ``--stat`` option.
+
 Parameters to convert subcommand:
 
 .. program:: qemu-img-convert
@@ -395,7 +402,7 @@ Command description:
 
   The rate limit for the commit process is specified by ``-r``.
 
-.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat [--block-size BLOCK_SIZE]] FILENAME1 FILENAME2
+.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat [--block-size BLOCK_SIZE]] [--shallow] FILENAME1 FILENAME2
 
   Check if two images have the same content. You can compare images with
   different format or settings.
diff --git a/qemu-img.c b/qemu-img.c
index 905150671f..b1cef4b7d1 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -85,6 +85,7 @@ enum {
     OPTION_SKIP_BROKEN = 277,
     OPTION_STAT = 278,
     OPTION_BLOCK_SIZE = 279,
+    OPTION_SHALLOW = 280,
 };
 
 typedef enum OutputFormat {
@@ -1483,7 +1484,7 @@ static int img_compare(int argc, char **argv)
     int64_t block_end;
     int ret = 0; /* return value - 0 Ident, 1 Different, >1 Error */
     bool progress = false, quiet = false, strict = false;
-    int flags;
+    int flags = 0;
     bool writethrough;
     int64_t total_size;
     int64_t offset = 0;
@@ -1504,6 +1505,7 @@ static int img_compare(int argc, char **argv)
             {"force-share", no_argument, 0, 'U'},
             {"stat", no_argument, 0, OPTION_STAT},
             {"block-size", required_argument, 0, OPTION_BLOCK_SIZE},
+            {"shallow", no_argument, 0, OPTION_SHALLOW},
             {0, 0, 0, 0}
         };
         c = getopt_long(argc, argv, ":hf:F:T:pqsU",
@@ -1569,6 +1571,9 @@ static int img_compare(int argc, char **argv)
                 exit(2);
             }
             break;
+        case OPTION_SHALLOW:
+            flags |= BDRV_O_NO_BACKING;
+            break;
         }
     }
 
@@ -1599,7 +1604,6 @@ static int img_compare(int argc, char **argv)
     /* Initialize before goto out */
     qemu_progress_init(progress, 2.0);
 
-    flags = 0;
     ret = bdrv_parse_cache_mode(cache, &flags, &writethrough);
     if (ret < 0) {
         error_report("Invalid source cache option: %s", cache);
diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index 96a193eea8..6b164767fd 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -40,9 +40,9 @@ SRST
 ERST
 
 DEF("compare", img_compare,
-    "compare [--object objectdef] [--image-opts] [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] [-U] [--stat [--block-size BLOCK_SIZE]] filename1 filename2")
+    "compare [--object objectdef] [--image-opts] [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] [-U] [--stat [--block-size BLOCK_SIZE]] [--shallow] filename1 filename2")
 SRST
-.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat [--block-size BLOCK_SIZE]] FILENAME1 FILENAME2
+.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat [--block-size BLOCK_SIZE]] [--shallow] FILENAME1 FILENAME2
 ERST
 
 DEF("convert", img_convert,
-- 
2.31.1

[PATCH v3 4/4] iotests: add qemu-img-compare-stat test

[Vladimir Sementsov-Ogievskiy]

Test new feature qemu-img compare --stat.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
---
 .../qemu-iotests/tests/qemu-img-compare-stat  |  88 +++++++++++++++
 .../tests/qemu-img-compare-stat.out           | 106 ++++++++++++++++++
 2 files changed, 194 insertions(+)
 create mode 100755 tests/qemu-iotests/tests/qemu-img-compare-stat
 create mode 100644 tests/qemu-iotests/tests/qemu-img-compare-stat.out

diff --git a/tests/qemu-iotests/tests/qemu-img-compare-stat b/tests/qemu-iotests/tests/qemu-img-compare-stat
new file mode 100755
index 0000000000..e2c0bcc7ef
--- /dev/null
+++ b/tests/qemu-iotests/tests/qemu-img-compare-stat
@@ -0,0 +1,88 @@
+#!/usr/bin/env python3
+#
+# Test qemu-img compare --stat
+#
+# Copyright (c) 2021 Virtuozzo International GmbH.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+import iotests
+from iotests import qemu_img_create, qemu_io, qemu_img_log, log
+
+iotests.script_initialize(supported_fmts=['qcow2'])
+
+a, b, c = iotests.file_path('a', 'b', 'c')
+
+log('= compare two images =\n')
+
+qemu_img_create('-f', iotests.imgfmt, a, '1M')
+qemu_img_create('-f', iotests.imgfmt, b, '1M')
+
+# equal data and zero
+qemu_io('-c', 'write -z 0 64K', a)
+qemu_io('-c', 'write -P 0 0 64K', b)
+
+# different data
+qemu_io('-c', 'write -P 1 64K 64K', a)
+qemu_io('-c', 'write -P 0 64K 64K', b)
+
+# equal data
+qemu_io('-c', 'write -P 2 128K 64K', a)
+qemu_io('-c', 'write -P 2 128K 64K', b)
+
+# equal unallocated and allocated zero
+qemu_io('-c', 'write -z 192K 64K', b)
+
+# unequal data and unallocated zero
+qemu_io('-c', 'write -P 3 256K 64K', a)
+
+qemu_img_log('compare', '--stat', a, b)
+
+log('\n= compare two increments =\n')
+
+qemu_img_create('-f', iotests.imgfmt, a, '1M')
+qemu_img_create('-f', iotests.imgfmt, '-b', a, '-F', iotests.imgfmt, b, '1M')
+qemu_img_create('-f', iotests.imgfmt, '-b', b, '-F', iotests.imgfmt, c, '1M')
+
+qemu_io('-c', 'write -P 1 0 1M', a)
+qemu_io('-c', 'write -P 2 0 64K', b)
+qemu_io('-c', 'write -P 3 64K 64K', c)
+qemu_img_log('compare', '--stat', b, c)
+
+log('\n= compare two increments with --shallow=\n')
+qemu_img_log('compare', '--stat', '--shallow', b, c)
+
+log('\n= compare images of different size =\n')
+qemu_img_create('-f', iotests.imgfmt, a, '1M')
+qemu_img_create('-f', iotests.imgfmt, b, '2M')
+qemu_io('-c', 'write -P 1 0 1M', a)
+qemu_io('-c', 'write -P 2 0 1M', b)
+qemu_io('-c', 'write -P 1 1M 64K', b)
+qemu_io('-c', f'write -z {1024 + 64 * 2}K 64K', b)
+qemu_io('-c', f'write -P 0 {1024 + 64 * 3}K 64K', b)
+qemu_img_log('compare', '--stat', a, b)
+
+log('\n= compare images with only 512 bytes different =\n')
+qemu_img_create('-f', iotests.imgfmt, a, '1M')
+qemu_img_create('-f', iotests.imgfmt, b, '1M')
+qemu_io('-c', 'write -P 1 0 1M', a)
+qemu_io('-c', 'write -P 2 0 512', b)
+qemu_io('-c', f'write -P 1 512 {1024 * 1024 - 512}', b)
+qemu_img_log('compare', '--stat', a, b)
+
+log('\n= compare images with only 512 bytes different, block-size=4K =\n')
+qemu_img_log('compare', '--stat', '--block-size', '4K', a, b)
+
+log('\n= end =')
diff --git a/tests/qemu-iotests/tests/qemu-img-compare-stat.out b/tests/qemu-iotests/tests/qemu-img-compare-stat.out
new file mode 100644
index 0000000000..93dd3aa194
--- /dev/null
+++ b/tests/qemu-iotests/tests/qemu-img-compare-stat.out
@@ -0,0 +1,106 @@
+= compare two images =
+
+Compare stats:
+Key
+D: DATA
+Z: ZERO
+A: ALLOCATED
+E: after end of file
+
+Equal:
+_Z__ -> _Z__ 720896 bytes (704 KiB) 68.8%
+_Z__ -> _ZA_ 65536 bytes (64 KiB) 6.2%
+D_A_ -> D_A_ 65536 bytes (64 KiB) 6.2%
+_ZA_ -> D_A_ 65536 bytes (64 KiB) 6.2%
+
+Unequal:
+D_A_ -> _Z__ 65536 bytes (64 KiB) 6.2%
+D_A_ -> D_A_ 65536 bytes (64 KiB) 6.2%
+
+
+= compare two increments =
+
+Compare stats:
+Key
+D: DATA
+Z: ZERO
+A: ALLOCATED
+E: after end of file
+
+Equal:
+D_A_ -> D_A_ 983040 bytes (960 KiB) 93.8%
+
+Unequal:
+D_A_ -> D_A_ 65536 bytes (64 KiB) 6.2%
+
+
+= compare two increments with --shallow=
+
+Compare stats:
+Key
+D: DATA
+Z: ZERO
+A: ALLOCATED
+E: after end of file
+
+Equal:
+_Z__ -> _Z__ 917504 bytes (896 KiB) 87.5%
+
+Unequal:
+_Z__ -> D_A_ 65536 bytes (64 KiB) 6.2%
+D_A_ -> _Z__ 65536 bytes (64 KiB) 6.2%
+
+
+= compare images of different size =
+
+Warning: Image size mismatch!
+Compare stats:
+Key
+D: DATA
+Z: ZERO
+A: ALLOCATED
+E: after end of file
+
+Equal:
+_Z_E -> _Z__ 851968 bytes (832 KiB) 40.6%
+_Z_E -> D_A_ 65536 bytes (64 KiB) 3.1%
+_Z_E -> _ZA_ 65536 bytes (64 KiB) 3.1%
+
+Unequal:
+D_A_ -> D_A_ 1048576 bytes (1 MiB) 50.0%
+_Z_E -> D_A_ 65536 bytes (64 KiB) 3.1%
+
+
+= compare images with only 512 bytes different =
+
+Compare stats:
+Key
+D: DATA
+Z: ZERO
+A: ALLOCATED
+E: after end of file
+
+Equal:
+D_A_ -> D_A_ 983040 bytes (960 KiB) 93.8%
+
+Unequal:
+D_A_ -> D_A_ 65536 bytes (64 KiB) 6.2%
+
+
+= compare images with only 512 bytes different, block-size=4K =
+
+Compare stats:
+Key
+D: DATA
+Z: ZERO
+A: ALLOCATED
+E: after end of file
+
+Equal:
+D_A_ -> D_A_ 1044480 bytes (0.996 MiB) 99.6%
+
+Unequal:
+D_A_ -> D_A_ 4096 bytes (4 KiB) 0.4%
+
+
+= end =
-- 
2.31.1

Re: [PATCH v3 1/4] qemu-img: implement compare --stat

[Eric Blake]

On Thu, Oct 28, 2021 at 12:24:38PM +0200, Vladimir Sementsov-Ogievskiy wrote:
> With new option qemu-img compare will not stop at first mismatch, but

With the new --stat option, qemu-img compare...

[Of course the subject line should be self-contained: think 'git
shortlog' and friends.  But I also argue the commit body should
generally be self-contained, rather than assuming you read the subject
line - why? because there are enough user interfaces out there
(including my email program) where the subject line is displayed
visually far away from the body, to the point that it is not always
safe to assume someone read the subject line.  If it feels too
redundant, visual tricks like starting the body with '...' force the
reader to realize they need to read the subject for full context, but
that comes with its own set of oddities]

> instead calculate statistics: how many clusters with different data,
> how many clusters with equal data, how many clusters were unallocated
> but become data and so on.
> 
> We compare images chunk by chunk. Chunk size depends on what
> block_status returns for both images. It may return less than cluster
> (remember about qcow2 subclusters), it may return more than cluster (if
> several consecutive clusters share same status). Finally images may
> have different cluster sizes. This all leads to ambiguity in how to
> finally compare the data.
> 
> What we can say for sure is that, when we compare two qcow2 images with
> same cluster size, we should compare clusters with data separately.
> Otherwise, if we for example compare 10 consecutive clusters of data
> where only one byte differs we'll report 10 different clusters.
> Expected result in this case is 1 different cluster and 9 equal ones.
> 
> So, to serve this case and just to have some defined rule let's do the
> following:
> 
> 1. Select some block-size for compare procedure. In this commit it must
>    be specified by user, next commit will add some automatic logic and
>    make --block-size optional.
> 
> 2. Go chunk-by-chunk using block_status as we do now with only one
>    differency:

difference

>    If block_status() returns DATA region that intersects block-size
>    aligned boundary, crop this region at this boundary.
> 
> This way it's still possible to compare less than cluster and report
> subcluster-level accuracy, but we newer compare more than one cluster
> of data.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  docs/tools/qemu-img.rst |  18 +++-
>  qemu-img.c              | 210 +++++++++++++++++++++++++++++++++++++---
>  qemu-img-cmds.hx        |   4 +-
>  3 files changed, 216 insertions(+), 16 deletions(-)
> 
> diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
> index d58980aef8..8b6b799dd4 100644
> --- a/docs/tools/qemu-img.rst
> +++ b/docs/tools/qemu-img.rst
> @@ -159,6 +159,18 @@ Parameters to compare subcommand:
>  
>    Strict mode - fail on different image size or sector allocation
>  
> +.. option:: --stat
> +
> +  Instead of exiting on the first mismatch, compare the whole images
> +  and print statistics on the amount of different pairs of blocks,
> +  based on their block status and whether they are equal or not.
> +
> +.. option:: --block-size BLOCK_SIZE
> +
> +  Block size for comparing with ``--stat``. This doesn't guarantee an
> +  exact size for comparing chunks, but it does guarantee that those
> +  chunks will never cross a block-size-aligned boundary.

Would it be safe to require that this be a power-of-2?  (If anything,
requiring now and relaxing later is better than allowing any number
now but later wishing it were a sane number)

> +
>  Parameters to convert subcommand:
>  
>  .. program:: qemu-img-convert
> @@ -378,7 +390,7 @@ Command description:
>  
>    The rate limit for the commit process is specified by ``-r``.
>  
> -.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] FILENAME1 FILENAME2
> +.. option:: compare [--object OBJECTDEF] [--image-opts] [-f FMT] [-F FMT] [-T SRC_CACHE] [-p] [-q] [-s] [-U] [--stat --block-size BLOCK_SIZE] FILENAME1 FILENAME2
>  
>    Check if two images have the same content. You can compare images with
>    different format or settings.
> @@ -405,9 +417,9 @@ Command description:
>    The following table sumarizes all exit codes of the compare subcommand:
>  
>    0
> -    Images are identical (or requested help was printed)
> +    Images are identical (or requested help was printed, or ``--stat`` was used)
>    1
> -    Images differ
> +    Images differ (1 is never returned when ``--stat`` option specified)

Why not?  Even when we print statistics, it's still easy to tell if
the data appears identical (block status might differ, but the guest
would see the same content), or had at least one difference.

>    2
>      Error on opening an image
>    3
> diff --git a/qemu-img.c b/qemu-img.c
> index f036a1d428..0cb7cebe91 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c

> +static void cmp_stat_print_status(int status)
> +{
> +    printf("%s%s%s%s",
> +           status & BDRV_BLOCK_DATA ? "D" : "_",
> +           status & BDRV_BLOCK_ZERO ? "Z" : "_",
> +           status & BDRV_BLOCK_ALLOCATED ? "A" : "_",
> +           status & BDRV_BLOCK_EOF ? "E" : "_");

Would this be more efficient with "%c%c%c%c" as the format, and using
'_' and friends below?

> @@ -1410,6 +1528,25 @@ static int img_compare(int argc, char **argv)
>      filename1 = argv[optind++];
>      filename2 = argv[optind++];
>  
> +    if (!stat && block_size) {
> +        error_report("--block-size can be used only together with --stat");
> +        ret = 2;
> +        goto out3;
> +    }
> +
> +    if (stat && !block_size) {
> +        /* TODO: make block-size optional */
> +        error_report("You must specify --block-size together with --stat");
> +        ret = 2;
> +        goto out3;
> +    }
> +
> +    if (stat && strict) {
> +        error_report("--stat can't be used together with -s");
> +        ret = 2;
> +        goto out3;
> +    }

Given this block...

>  
>          assert(pnum1 && pnum2);
>          chunk = MIN(pnum1, pnum2);
>  
> -        if (strict) {
> +        if (strict && !stat) {

...the check for !stat here is dead.


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [PATCH v3 2/4] qemu-img: make --block-size optional for compare --stat

[Eric Blake]

On Thu, Oct 28, 2021 at 12:24:39PM +0200, Vladimir Sementsov-Ogievskiy wrote:
> Let's detect block-size automatically if not specified by user:
> 
>  If both files define cluster-size, use minimum to be more precise.
>  If both files don't specify cluster-size, use default of 64K
>  If only one file specify cluster-size, just use it.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  docs/tools/qemu-img.rst |  7 +++-
>  qemu-img.c              | 71 +++++++++++++++++++++++++++++++++++++----
>  qemu-img-cmds.hx        |  4 +--
>  3 files changed, 72 insertions(+), 10 deletions(-)
>

Reviewed-by: Eric Blake <eblake@redhat.com>

> +    if (cluster_size1 > 0 && cluster_size2 > 0) {
> +        if (cluster_size1 == cluster_size2) {
> +            block_size = cluster_size1;
> +        } else {
> +            block_size = MIN(cluster_size1, cluster_size2);
> +            qprintf(quiet, "%s and %s have different cluster sizes: %d and %d "
> +                    "respectively. Using minimum as block-size for "
> +                    "accuracy: %d. %s\n",
> +                    fname1, fname2, cluster_size1,
> +                    cluster_size2, block_size, note);

Results in a long line; I don't know if it's worth trying to wrap it
(if we had a generic utility function that took arbitrary text, then
outputs it wrapped to the user's current terminal column width, I'd
suggest using that instead - but that's NOT something I expect you to
write, and I don't know if glib has such a utility).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [PATCH v3 3/4] qemu-img: add --shallow option for qemu-img compare

[Eric Blake]

On Thu, Oct 28, 2021 at 12:24:40PM +0200, Vladimir Sementsov-Ogievskiy wrote:
> Allow compare only top images of backing chains. This is useful to

Allow the comparison of only the top image of backing chains.

> compare images with same backing file or to compare incremental images
> from the chain of incremental backups with "--stat" option.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Reviewed-by: Hanna Reitz <hreitz@redhat.com>
> ---
>  docs/tools/qemu-img.rst | 9 ++++++++-
>  qemu-img.c              | 8 ++++++--
>  qemu-img-cmds.hx        | 4 ++--
>  3 files changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
> index 9bfdd93d6c..c6e9306c70 100644
> --- a/docs/tools/qemu-img.rst
> +++ b/docs/tools/qemu-img.rst
> @@ -176,6 +176,13 @@ Parameters to compare subcommand:
>      - If both files don't specify cluster-size, use default of 64K
>      - If only one file specifies cluster-size, just use that.
>  
> +.. option:: --shallow
> +
> +  This option prevents opening and comparing any backing files.
> +  This is useful to compare images with same backing file or to compare
> +  incremental images from the chain of incremental backups with
> +  ``--stat`` option.

If I understand correctly, your implementation makes --shallow an
all-or-none option (either both images are compared shallow, or
neither is).  Does it make sense to make it a per-image option
(--shallow-source, --shallow-dest), where --shallow is a synonym for
the more verbose --shallow-source --shallow-dest?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [PATCH v3 2/4] qemu-img: make --block-size optional for compare --stat

[Vladimir Sementsov-Ogievskiy]

29.10.2021 23:32, Eric Blake wrote:
> On Thu, Oct 28, 2021 at 12:24:39PM +0200, Vladimir Sementsov-Ogievskiy wrote:
>> Let's detect block-size automatically if not specified by user:
>>
>>   If both files define cluster-size, use minimum to be more precise.
>>   If both files don't specify cluster-size, use default of 64K
>>   If only one file specify cluster-size, just use it.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> ---
>>   docs/tools/qemu-img.rst |  7 +++-
>>   qemu-img.c              | 71 +++++++++++++++++++++++++++++++++++++----
>>   qemu-img-cmds.hx        |  4 +--
>>   3 files changed, 72 insertions(+), 10 deletions(-)
>>
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 
>> +    if (cluster_size1 > 0 && cluster_size2 > 0) {
>> +        if (cluster_size1 == cluster_size2) {
>> +            block_size = cluster_size1;
>> +        } else {
>> +            block_size = MIN(cluster_size1, cluster_size2);
>> +            qprintf(quiet, "%s and %s have different cluster sizes: %d and %d "
>> +                    "respectively. Using minimum as block-size for "
>> +                    "accuracy: %d. %s\n",
>> +                    fname1, fname2, cluster_size1,
>> +                    cluster_size2, block_size, note);
> 
> Results in a long line; I don't know if it's worth trying to wrap it
> (if we had a generic utility function that took arbitrary text, then
> outputs it wrapped to the user's current terminal column width, I'd
> suggest using that instead - but that's NOT something I expect you to
> write, and I don't know if glib has such a utility).
> 

Hmm. But long lines printed to the terminal are wrapped by terminal automatically, so we don't need to wrap to terminal width by hand..

-- 
Best regards,
Vladimir

Re: [PATCH v3 3/4] qemu-img: add --shallow option for qemu-img compare

[Vladimir Sementsov-Ogievskiy]

29.10.2021 23:44, Eric Blake wrote:
> On Thu, Oct 28, 2021 at 12:24:40PM +0200, Vladimir Sementsov-Ogievskiy wrote:
>> Allow compare only top images of backing chains. This is useful to
> 
> Allow the comparison of only the top image of backing chains.
> 
>> compare images with same backing file or to compare incremental images
>> from the chain of incremental backups with "--stat" option.
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> Reviewed-by: Hanna Reitz <hreitz@redhat.com>
>> ---
>>   docs/tools/qemu-img.rst | 9 ++++++++-
>>   qemu-img.c              | 8 ++++++--
>>   qemu-img-cmds.hx        | 4 ++--
>>   3 files changed, 16 insertions(+), 5 deletions(-)
>>
>> diff --git a/docs/tools/qemu-img.rst b/docs/tools/qemu-img.rst
>> index 9bfdd93d6c..c6e9306c70 100644
>> --- a/docs/tools/qemu-img.rst
>> +++ b/docs/tools/qemu-img.rst
>> @@ -176,6 +176,13 @@ Parameters to compare subcommand:
>>       - If both files don't specify cluster-size, use default of 64K
>>       - If only one file specifies cluster-size, just use that.
>>   
>> +.. option:: --shallow
>> +
>> +  This option prevents opening and comparing any backing files.
>> +  This is useful to compare images with same backing file or to compare
>> +  incremental images from the chain of incremental backups with
>> +  ``--stat`` option.
> 
> If I understand correctly, your implementation makes --shallow an
> all-or-none option (either both images are compared shallow, or
> neither is).  Does it make sense to make it a per-image option
> (--shallow-source, --shallow-dest), where --shallow is a synonym for
> the more verbose --shallow-source --shallow-dest?
> 

Usable, to compare incremental image with "everything below it".

But I'm not sure about source/dest terms in context of compare, where image roles are symmetrical.

I even start to thing, that it should be an option, used together with --image-opts, applied to image in person.. And actually we already have it, like

--image-opts ... driver=qcow2,file.filename=file.qcow2,backing=

At least this works with qemu-io. But prints warning:

>> qemu-io: warning: Use of "backing": "" is deprecated; use "backing": null instead

And of course, "null" doesn't work here.

May be we should drop the warning, keeping backing= syntax at least for --image-opts of qemu utilities. Or, another way, support json for --image-opts.

What do you think? driver=qcow2,file.filename=a.qcow2,backing=  doesn't look better than --shallow. But if we want to make shallow option per-image, we can't ignore the fact that we already have a way to specify per-image options.


-- 
Best regards,
Vladimir

Re: [PATCH v3 2/4] qemu-img: make --block-size optional for compare --stat

[Eric Blake]

On Mon, Nov 01, 2021 at 11:03:22AM +0300, Vladimir Sementsov-Ogievskiy wrote:
> 29.10.2021 23:32, Eric Blake wrote:
> > On Thu, Oct 28, 2021 at 12:24:39PM +0200, Vladimir Sementsov-Ogievskiy wrote:
> > > Let's detect block-size automatically if not specified by user:
> > > 
> > >   If both files define cluster-size, use minimum to be more precise.
> > >   If both files don't specify cluster-size, use default of 64K
> > >   If only one file specify cluster-size, just use it.
> > > 
> > > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> > > ---
> > >   docs/tools/qemu-img.rst |  7 +++-
> > >   qemu-img.c              | 71 +++++++++++++++++++++++++++++++++++++----
> > >   qemu-img-cmds.hx        |  4 +--
> > >   3 files changed, 72 insertions(+), 10 deletions(-)
> > > 
> > 
> > Reviewed-by: Eric Blake <eblake@redhat.com>
> > 
> > > +    if (cluster_size1 > 0 && cluster_size2 > 0) {
> > > +        if (cluster_size1 == cluster_size2) {
> > > +            block_size = cluster_size1;
> > > +        } else {
> > > +            block_size = MIN(cluster_size1, cluster_size2);
> > > +            qprintf(quiet, "%s and %s have different cluster sizes: %d and %d "
> > > +                    "respectively. Using minimum as block-size for "
> > > +                    "accuracy: %d. %s\n",
> > > +                    fname1, fname2, cluster_size1,
> > > +                    cluster_size2, block_size, note);
> > 
> > Results in a long line; I don't know if it's worth trying to wrap it
> > (if we had a generic utility function that took arbitrary text, then
> > outputs it wrapped to the user's current terminal column width, I'd
> > suggest using that instead - but that's NOT something I expect you to
> > write, and I don't know if glib has such a utility).
> > 
> 
> Hmm. But long lines printed to the terminal are wrapped by terminal automatically, so we don't need to wrap to terminal width by hand..

/me using a short line length in the next paragraph on purpose...

There's a difference between the ter
minal wrapping when you hit the maxi
mum length, and in intelligent
wrapping the prefers natural word
breaks.

There are programs out there that do intelligent wrapping (for
example, the mutt mailer), but I'm not sure if those wrapping routines
are available through glib.  At any rate, I do NOT want to reimplement
intelligent wrapping from scratch (Unicode specifies a rather complex
algorithm for getting sane wrapping in the presence of various Unicode
characters, and it is not trivial https://unicode.org/reports/tr14/).
So unless someone knows of an easy-to-use library that does wrapping,
you are right that leaving long lines for the terminal to output, even
when that output has awkward mid-word breaks, is tolerable.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [PATCH v3 1/4] qemu-img: implement compare --stat

[Hanna Reitz]

On 28.10.21 12:24, Vladimir Sementsov-Ogievskiy wrote:
> With new option qemu-img compare will not stop at first mismatch, but
> instead calculate statistics: how many clusters with different data,
> how many clusters with equal data, how many clusters were unallocated
> but become data and so on.
>
> We compare images chunk by chunk. Chunk size depends on what
> block_status returns for both images. It may return less than cluster
> (remember about qcow2 subclusters), it may return more than cluster (if
> several consecutive clusters share same status). Finally images may
> have different cluster sizes. This all leads to ambiguity in how to
> finally compare the data.
>
> What we can say for sure is that, when we compare two qcow2 images with
> same cluster size, we should compare clusters with data separately.
> Otherwise, if we for example compare 10 consecutive clusters of data
> where only one byte differs we'll report 10 different clusters.
> Expected result in this case is 1 different cluster and 9 equal ones.
>
> So, to serve this case and just to have some defined rule let's do the
> following:
>
> 1. Select some block-size for compare procedure. In this commit it must
>     be specified by user, next commit will add some automatic logic and
>     make --block-size optional.
>
> 2. Go chunk-by-chunk using block_status as we do now with only one
>     differency:
>     If block_status() returns DATA region that intersects block-size
>     aligned boundary, crop this region at this boundary.
>
> This way it's still possible to compare less than cluster and report
> subcluster-level accuracy, but we newer compare more than one cluster
> of data.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   docs/tools/qemu-img.rst |  18 +++-
>   qemu-img.c              | 210 +++++++++++++++++++++++++++++++++++++---
>   qemu-img-cmds.hx        |   4 +-
>   3 files changed, 216 insertions(+), 16 deletions(-)

[...]

> diff --git a/qemu-img.c b/qemu-img.c
> index f036a1d428..0cb7cebe91 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c

[...]

> @@ -1465,7 +1602,7 @@ static int img_compare(int argc, char **argv)
>       }
>   
>       while (offset < total_size) {
> -        int status1, status2;
> +        block_end = QEMU_ALIGN_UP(offset + 1, block_size);

Without --stat, `block_size` is 0, and then this is a division by zero.

My compiler seems clever enough to skip this division if `stat == NULL`, 
but when I add a `printf("%li\n", block_size);` after this line and do a 
compare without --stat, qemu-img aborts.  I don’t think we should rely 
on the compiler optimization working here.

(Sorry I didn’t notice this in v2, I just noticed it because I was 
trying to find out whether `block_size` really needs to be a power of 
two as Eric proposed...  The good news is that I don’t think it needs to 
be a power of two (still might make sense to require it), but, well, the 
bad news is that I found this.)

Hanna

Re: [PATCH v3 2/4] qemu-img: make --block-size optional for compare --stat

[Hanna Reitz]

On 28.10.21 12:24, Vladimir Sementsov-Ogievskiy wrote:
> Let's detect block-size automatically if not specified by user:
>
>   If both files define cluster-size, use minimum to be more precise.
>   If both files don't specify cluster-size, use default of 64K
>   If only one file specify cluster-size, just use it.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   docs/tools/qemu-img.rst |  7 +++-
>   qemu-img.c              | 71 +++++++++++++++++++++++++++++++++++++----
>   qemu-img-cmds.hx        |  4 +--
>   3 files changed, 72 insertions(+), 10 deletions(-)

Reviewed-by: Hanna Reitz <hreitz@redhat.com>