[Qemu-devel] [PATCH][RFC] Add compare subcommand for qemu-img

[Miroslav Rezanina <mrezanin@redhat.com>]

This patch adds compare subcommand that compares two images. Compare has following criteria:
- only data part is compared
- unallocated sectors are not read
- in case of different image size, exceeding part of bigger disk has to be zeroed/unallocated to compare rest
- qemu-img returns:
   - 0 if images are identical
   - 1 if images differ
   - 2 on error

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

Patch:
--
diff --git a/block.c b/block.c
index b38940b..919f8e9 100644
--- a/block.c
+++ b/block.c
@@ -2284,6 +2284,7 @@ int bdrv_has_zero_init(BlockDriverState *bs)
 
 typedef struct BdrvCoIsAllocatedData {
     BlockDriverState *bs;
+    BlockDriverState *base;
     int64_t sector_num;
     int nb_sectors;
     int *pnum;
@@ -2414,6 +2415,44 @@ int coroutine_fn bdrv_co_is_allocated_above(BlockDriverState *top,
     return 0;
 }
 
+/* Coroutine wrapper for bdrv_is_allocated_above() */
+static void coroutine_fn bdrv_is_allocated_above_co_entry(void *opaque)
+{
+    BdrvCoIsAllocatedData *data = opaque;
+    BlockDriverState *top = data->bs;
+    BlockDriverState *base = data->base;
+
+    data->ret = bdrv_co_is_allocated_above(top, base, data->sector_num,
+                                           data->nb_sectors,data->pnum);
+    data->done = true;
+}
+
+/*
+ * Synchronous wrapper around bdrv_co_is_allocated_above().
+ *
+ * See bdrv_co_is_allocated_above() for details.
+ */
+int bdrv_is_allocated_above(BlockDriverState *top, BlockDriverState *base,
+                      int64_t sector_num, int nb_sectors, int *pnum)
+{
+    Coroutine *co;
+    BdrvCoIsAllocatedData data = {
+        .bs = top,
+        .base = base,
+        .sector_num = sector_num,
+        .nb_sectors = nb_sectors,
+        .pnum = pnum,
+        .done = false,
+    };
+
+    co = qemu_coroutine_create(bdrv_is_allocated_above_co_entry);
+    qemu_coroutine_enter(co, &data);
+    while (!data.done) {
+        qemu_aio_wait();
+    }
+    return data.ret;
+}
+
 BlockInfoList *qmp_query_block(Error **errp)
 {
     BlockInfoList *head = NULL, *cur_item = NULL;
diff --git a/block.h b/block.h
index c89590d..6f39da9 100644
--- a/block.h
+++ b/block.h
@@ -256,7 +256,8 @@ int bdrv_co_discard(BlockDriverState *bs, int64_t sector_num, int nb_sectors);
 int bdrv_has_zero_init(BlockDriverState *bs);
 int bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
                       int *pnum);
-
+int bdrv_is_allocated_above(BlockDriverState* top, BlockDriverState *base,
+                            int64_t sector_num, int nb_sectors, int *pnum);
 void bdrv_set_on_error(BlockDriverState *bs, BlockErrorAction on_read_error,
                        BlockErrorAction on_write_error);
 BlockErrorAction bdrv_get_on_error(BlockDriverState *bs, int is_read);
diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index 39419a0..5b34896 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -27,6 +27,12 @@ STEXI
 @item commit [-f @var{fmt}] [-t @var{cache}] @var{filename}
 ETEXI
 
+DEF("compare", img_compare,
+    "compare [-f fmt] [-g fmt] [-p] filename1 filename2")
+STEXI
+@item compare [-f fmt] [-g fmt] [-p] filename1 filename2
+ETEXI
+
 DEF("convert", img_convert,
     "convert [-c] [-p] [-f fmt] [-t cache] [-O output_fmt] [-o options] [-s snapshot_name] [-S sparse_size] filename [filename2 [...]] output_filename")
 STEXI
diff --git a/qemu-img.c b/qemu-img.c
index 80cfb9b..99a2f16 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -96,7 +96,9 @@ static void help(void)
            "  '-a' applies a snapshot (revert disk to saved state)\n"
            "  '-c' creates a snapshot\n"
            "  '-d' deletes a snapshot\n"
-           "  '-l' lists all snapshots in the given image\n";
+           "  '-l' lists all snapshots in the given image\n"
+           "Parameters to compare subcommand:\n"
+           "  '-g' Second image format (in case it differs from first image)\n";
 
     printf("%s\nSupported formats:", help_msg);
     bdrv_iterate_format(format_print, NULL);
@@ -652,6 +654,223 @@ static int compare_sectors(const uint8_t *buf1, const uint8_t *buf2, int n,
 
 #define IO_BUF_SIZE (2 * 1024 * 1024)
 
+/*
+ * Get number of sectors that can be stored in IO buffer.
+ */
+
+static int64_t sectors_to_process(int64_t total, int64_t from)
+{
+  int64_t rv = total - from;
+
+  if (rv > (IO_BUF_SIZE >> BDRV_SECTOR_BITS))
+     return IO_BUF_SIZE >> BDRV_SECTOR_BITS;
+
+  return rv;
+}
+
+/*
+ * Compares two images. Exit codes:
+ *
+ * 0 - Images are identical
+ * 1 - Images differ
+ * 2 - Error occured
+ */
+
+static int img_compare(int argc, char **argv)
+{
+    const char *fmt1 = NULL, *fmt2 = NULL, *filename1, *filename2;
+    BlockDriverState *bs1, *bs2;
+    int64_t total_sectors1, total_sectors2;
+    uint8_t *buf1 = NULL, *buf2 = NULL;
+    int pnum1, pnum2;
+    int allocated1,allocated2;
+    int flags = BDRV_O_FLAGS;
+    int progress=0,ret = 0; /* return value - 0 Ident, 1 Different, 2 Error */
+    int64_t total_sectors;
+    int64_t sector_num = 0;
+    int64_t nb_sectors;
+    int c, rv, pnum;
+    uint64_t bs_sectors;
+    uint64_t progress_base;
+
+
+    for(;;) {
+        c = getopt(argc, argv, "pf:g:");
+        if (c == -1) {
+            break;
+        }
+        switch(c) {
+        case 'f':
+            fmt1 = optarg;
+            if (fmt2 == NULL)
+                fmt2 = optarg;
+            break;
+        case 'g':
+            fmt2 = optarg;
+            break;
+        case 'p':
+            progress = 1;
+            break;
+        }
+    }
+    if (optind >= argc) {
+        help();
+        goto out3;
+    }
+    filename1 = argv[optind++];
+    filename2 = argv[optind++];
+
+    /* Initialize before goto out */
+    qemu_progress_init(progress, 2.0);
+
+    bs1 = bdrv_new_open(filename1, fmt1, flags);
+    if (!bs1) {
+      error_report("Can't open file %s", filename1);
+      ret = 2;
+      goto out3;
+    }
+
+    bs2 = bdrv_new_open(filename2, fmt2, flags);
+    if (!bs2) {
+      error_report("Can't open file %s:",filename2);
+      ret = 2;
+      goto out2;
+    }
+
+    qemu_progress_print(0, 100);
+
+    buf1 = qemu_blockalign(bs1,IO_BUF_SIZE);
+    buf2 = qemu_blockalign(bs2,IO_BUF_SIZE);
+    bdrv_get_geometry(bs1,&bs_sectors);
+    total_sectors1 = bs_sectors;
+    bdrv_get_geometry(bs2,&bs_sectors);
+    total_sectors2 = bs_sectors;
+    total_sectors = total_sectors1;
+    progress_base = total_sectors;
+
+    if (total_sectors1 != total_sectors2) {
+        BlockDriverState *bsover;
+        int64_t over_sectors, over_num;
+        const char *filename_over;
+
+        if (total_sectors1 > total_sectors2) {
+            total_sectors = total_sectors2;
+            over_sectors = total_sectors1;
+            over_num = total_sectors2;
+            bsover = bs1;
+            filename_over = filename1;
+        } else {
+            total_sectors = total_sectors1;
+            over_sectors = total_sectors2;
+            over_num = total_sectors1;
+            bsover = bs1;
+            filename_over = filename2;
+        }
+
+        progress_base = over_sectors;
+
+        for (;;) {
+            if ((nb_sectors = sectors_to_process(over_sectors,over_num)) <= 0)
+              break;
+
+            rv = bdrv_is_allocated(bsover,over_num,nb_sectors,&pnum);
+            nb_sectors = pnum;
+            if (rv) {
+               rv = bdrv_read(bsover, over_num, buf1, nb_sectors);
+               if (rv < 0) {
+                   error_report("error while reading sector %" PRId64 " of %s:"
+                                " %s",over_num, filename_over, strerror(-rv));
+                   ret = 2;
+                   goto out;
+               }
+               rv = is_allocated_sectors(buf1, nb_sectors, &pnum);
+               if (rv || pnum != nb_sectors) {
+                   ret = 1;
+                   printf("Images are different - image size mismatch!\n");
+                   goto out;
+               }
+            }
+            over_num += nb_sectors;
+            qemu_progress_print(((float) nb_sectors / progress_base)*100, 100);
+        }
+    }
+
+    for (;;) {
+        if ((nb_sectors = sectors_to_process(total_sectors, sector_num)) <= 0)
+            break;
+        allocated1 = bdrv_is_allocated_above(bs1, NULL, sector_num, nb_sectors,
+                                             &pnum1);
+        allocated2 = bdrv_is_allocated_above(bs2, NULL, sector_num, nb_sectors,
+                                             &pnum2);
+        if (pnum1 < pnum2) {
+            nb_sectors = pnum1;
+        } else {
+            nb_sectors = pnum2;
+        }
+
+        if (allocated1 == allocated2) {
+            if (allocated1) {
+              rv = bdrv_read(bs1, sector_num, buf1, nb_sectors);
+              if (rv < 0) {
+                  ret = 2;
+                  error_report("error while reading sector %" PRId64 " of %s:"
+                               " %s", sector_num, filename1, strerror(-rv));
+                  goto out;
+              }
+              rv = bdrv_read(bs2,sector_num,buf2, nb_sectors);
+              if (rv < 0) {
+                  ret = 2;
+                  error_report("error while reading sector %" PRId64 " of %s:"
+                               " %s", sector_num, filename2, strerror(-rv));
+                  goto out;
+              }
+              rv = compare_sectors(buf1,buf2,nb_sectors,&pnum);
+              if (rv || pnum != nb_sectors) {
+                  ret = 1;
+                  printf("Images are different - content mismatch!\n");
+                  goto out;
+              }
+            }
+        } else {
+           BlockDriverState *bstmp;
+           const char* filenametmp;
+           if (allocated1) {
+               bstmp = bs1;
+               filenametmp = filename1;
+           } else {
+               bstmp = bs2;
+               filenametmp = filename2;
+           }
+           rv = bdrv_read(bstmp, sector_num, buf1, nb_sectors);
+           if (rv < 0) {
+               ret = 2;
+               error_report("error while reading sector %" PRId64 " of %s: %s",
+                               sector_num, filenametmp, strerror(-rv));
+               goto out;
+           }
+           rv = is_allocated_sectors(buf1, nb_sectors, &pnum);
+           if (rv || pnum != nb_sectors) {
+               ret = 1;
+               printf("Images are different - content mismatch!\n");
+               goto out;
+           }
+        }
+        sector_num += nb_sectors;
+        qemu_progress_print(((float) nb_sectors / progress_base)*100, 100);
+    }
+    printf("Images are identical.\n");
+
+out:
+    bdrv_delete(bs2);
+    qemu_vfree(buf1);
+    qemu_vfree(buf2);
+out2:
+    bdrv_delete(bs1);
+out3:
+    qemu_progress_end();
+    return ret;
+}
+
 static int img_convert(int argc, char **argv)
 {
     int c, ret = 0, n, n1, bs_n, bs_i, compress, cluster_size, cluster_sectors;
-- 
Miroslav Rezanina
Software Engineer - Virtualization Team - XEN kernel