[Qemu-devel] [PATCH v5] Add compare subcommand for qemu-img

[Miroslav Rezanina]

This is second version of  patch adding 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

v5 (only minor changes):
 - removed redundant comment
 - removed dead code (goto after help())
 - set final total_sectors on first assignment

v4:
 - Fixed various typos
 - Added functions for empty sector check and sector-to-bytes offset conversion
 - Fixed command-line parameters processing

v3:
 - options -f/-F are orthogonal
 - documentation updated to new syntax and behavior
 - used byte offset instead of sector number for output
 
v2:
 - changed option for second image format to -F
 - changed handling of -f and -F [1]
 - added strict mode (-s)
 - added quiet mode (-q)
 - improved output messages [2]
 - rename variables for larger image handling
 - added man page content

Signed-off-by: Miroslav Rezanina <address@hidden>

Note: Do not move any code to separate function as suggested by Stefan. Code to 
extract is not reusable and
require access to some of local variables (for error handling part). Only code 
in separate function is the 
checking passed sectors for zero value as this can be reused on two places in 
the function.


diff --git a/block.c b/block.c
index 854ebd6..fdc8c45 100644
--- a/block.c
+++ b/block.c
@@ -2698,6 +2698,7 @@ int bdrv_has_zero_init(BlockDriverState *bs)
 
 typedef struct BdrvCoIsAllocatedData {
     BlockDriverState *bs;
+    BlockDriverState *base;
     int64_t sector_num;
     int nb_sectors;
     int *pnum;
@@ -2828,6 +2829,44 @@ 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;
+}
+
 BlockInfo *bdrv_query_info(BlockDriverState *bs)
 {
     BlockInfo *info = g_malloc0(sizeof(*info));
diff --git a/block.h b/block.h
index 722c620..2cb8d71 100644
--- a/block.h
+++ b/block.h
@@ -278,6 +278,8 @@ 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, BlockdevOnError on_read_error,
                        BlockdevOnError on_write_error);
diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index a181363..c076085 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] [-F fmt] [-p] [-q] [-s] filename1 filename2")
+STEXI
address@hidden compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-q] [-s] 
@var{filename1} @var{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 e29e01b..6cad518 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -101,7 +101,13 @@ 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"
+           "\n"
+           "Parameters to compare subcommand:\n"
+           "  '-f' First image format\n"
+           "  '-F' Second image format\n"
+           "  '-q' Quiet mode - do not print any output (except errors)\n"
+           "  '-s' Strict mode - fail on different image size or sector 
allocation\n";
 
     printf("%s\nSupported formats:", help_msg);
     bdrv_iterate_format(format_print, NULL);
@@ -658,6 +664,282 @@ static int compare_sectors(const uint8_t *buf1, const 
uint8_t *buf2, int n,
 
 #define IO_BUF_SIZE (2 * 1024 * 1024)
 
+static int64_t sectors_to_bytes(int64_t sectors)
+{
+    return sectors << BDRV_SECTOR_BITS;
+}
+
+/*
+ * 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;
+}
+
+/*
+ * Check if passed sectors are filled with 0.
+ *
+ * Returns 0 in case sectors are filled with 0, 1 if sectors contain non-zero
+ * data and negative value on error.
+ */
+static int is_zeroed(BlockDriverState *bs, int64_t sect_num, int sect_count,
+              const char *filename, uint8_t *buffer, int quiet)
+{
+    int pnum, rv = 0;
+    rv = bdrv_read(bs, sect_num, buffer, sect_count);
+    if (rv < 0) {
+        error_report("Error while reading offset %" PRId64 " of %s: %s",
+                     sectors_to_bytes(sect_num), filename, strerror(-rv));
+        return rv;
+    }
+    rv = is_allocated_sectors(buffer, sect_count, &pnum);
+    if (rv || pnum != sect_count) {
+        if (!quiet) {
+            printf("Content mismatch at offset %" PRId64 "!\n",
+                   sectors_to_bytes(rv ? sect_num : sect_num + pnum));
+        }
+        return 1;
+    }
+
+    return 0;
+}
+
+/*
+ * Compares two images. Exit codes:
+ *
+ * 0 - Images are identical
+ * 1 - Images differ
+ * 2 - Error occurred
+ */
+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 ret = 0; /* return value - 0 Ident, 1 Different, 2 Error */
+    int progress = 0, quiet = 0, strict = 0;
+    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:F:sq");
+        if (c == -1) {
+            break;
+        }
+        switch (c) {
+        case 'f':
+            fmt1 = optarg;
+            break;
+        case 'F':
+            fmt2 = optarg;
+            break;
+        case 'p':
+            progress = 1;
+            break;
+        case 'q':
+            quiet = 1;
+            break;
+        case 's':
+            strict = 1;
+            break;
+        }
+    }
+
+    /* Progress is not shown in Quiet mode */
+    if (quiet) {
+        progress = 0;
+    }
+
+    if (optind > argc - 2) {
+        help();
+    }
+    filename1 = argv[optind++];
+    filename2 = argv[optind++];
+
+    /* Initialize before goto out */
+    qemu_progress_init(progress, 2.0);
+
+    bs1 = bdrv_new_open(filename1, fmt1, flags, true);
+    if (!bs1) {
+        error_report("Can't open file %s", filename1);
+        ret = 2;
+        goto out3;
+    }
+
+    bs2 = bdrv_new_open(filename2, fmt2, flags, true);
+    if (!bs2) {
+        error_report("Can't open file %s", filename2);
+        ret = 2;
+        goto out2;
+    }
+
+    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 = MIN(total_sectors1, total_sectors2);
+    progress_base = total_sectors;
+
+    qemu_progress_print(0, 100);
+
+    if (total_sectors1 != total_sectors2) {
+        BlockDriverState *bsover;
+        int64_t lo_total_sectors, lo_sector_num;
+        const char *filename_over;
+
+        if (strict) {
+            ret = 1;
+            if (!quiet) {
+                printf("Strict mode: Image size mismatch!\n");
+            }
+            goto out;
+        } else {
+            error_report("Image size mismatch!");
+        }
+
+        if (total_sectors1 > total_sectors2) {
+            lo_total_sectors = total_sectors1;
+            lo_sector_num = total_sectors2;
+            bsover = bs1;
+            filename_over = filename1;
+        } else {
+            lo_total_sectors = total_sectors2;
+            lo_sector_num = total_sectors1;
+            bsover = bs2;
+            filename_over = filename2;
+        }
+
+        progress_base = lo_total_sectors;
+
+        for (;;) {
+            nb_sectors = sectors_to_process(lo_total_sectors, lo_sector_num);
+            if (nb_sectors <= 0) {
+                break;
+            }
+            rv = bdrv_is_allocated_above(bsover, NULL, lo_sector_num,
+                                         nb_sectors, &pnum);
+            nb_sectors = pnum;
+            if (rv) {
+                rv = is_zeroed(bsover, lo_sector_num, nb_sectors,
+                               filename_over, buf1, quiet);
+                if (rv) {
+                    if (rv < 0) {
+                        ret = 2;
+                    }
+                    goto out;
+                }
+            }
+            lo_sector_num += nb_sectors;
+            qemu_progress_print(((float) nb_sectors / progress_base)*100, 100);
+        }
+    }
+
+
+    for (;;) {
+        nb_sectors = sectors_to_process(total_sectors, sector_num);
+        if (nb_sectors <= 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 offset %" PRId64 " of 
%s:"
+                                 " %s", sectors_to_bytes(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 offset %" PRId64
+                                 " of %s: %s", sectors_to_bytes(sector_num),
+                                 filename2, strerror(-rv));
+                    goto out;
+                }
+                rv = compare_sectors(buf1, buf2, nb_sectors, &pnum);
+                if (rv || pnum != nb_sectors) {
+                    ret = 1;
+                    if (!quiet) {
+                        printf("Content mismatch at offset %" PRId64 "!\n",
+                               sectors_to_bytes(
+                                   rv ? sector_num : sector_num + pnum));
+                    }
+                    goto out;
+                }
+            }
+        } else {
+            if (strict) {
+                ret = 1;
+                if (!quiet) {
+                    printf("Strict mode: Offset %" PRId64
+                           " allocation mismatch!",
+                           sectors_to_bytes(sector_num));
+                }
+                goto out;
+            }
+
+            if (allocated1) {
+                rv = is_zeroed(bs1, sector_num, nb_sectors,
+                               filename1, buf1, quiet);
+            } else {
+                rv = is_zeroed(bs2, sector_num, nb_sectors,
+                               filename2, buf1, quiet);
+            }
+            if (rv) {
+                if (rv < 0) {
+                    ret = 2;
+                }
+                goto out;
+            }
+        }
+        sector_num += nb_sectors;
+        qemu_progress_print(((float) nb_sectors / progress_base)*100, 100);
+    }
+    if (!quiet) {
+        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;
diff --git a/qemu-img.texi b/qemu-img.texi
index 60b83fc..cb073c3 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -81,6 +81,20 @@ deletes a snapshot
 lists all snapshots in the given image
 @end table
 
+Parameters to compare subcommand:
+
address@hidden @option
+
address@hidden -f
+First image format
address@hidden -F
+Second image format
address@hidden -q
+Quiet mode - do not print any output (except errors)
address@hidden -s
+Strict mode - fail on on different image size or sector allocation
address@hidden table
+
 Command description:
 
 @table @option
@@ -114,6 +128,28 @@ it doesn't need to be specified separately in this case.
 
 Commit the changes recorded in @var{filename} in its base image.
 
address@hidden compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] 
@var{filename1} @var{filename2}
+
+Check if two images contains same content. You can compare images with
+different format or settings.
+
+Format is probed unless you specify it by @var{-f} (used for @var{filename1}) 
and/or @var{-F} (used for @var{filename2}) option.
+
+By default, compare evaluates as identical images with different size where
+bigger image contains only unallocated and/or zeroed sectors in area above
+second image size. In addition, if any sector is not allocated in one image
+and contains only zero bytes in second, it is evaluated as equal. You can use
+Strict mode by specifying @var{-s} option. When compare runs in Strict mode,
+it fails in case image size differs or sector is allocated in one image and
+is not allocated in second.
+
+By default, compare prints out result message. This message displays
+information that both images are same or position of first different byte.
+In addition, result message can report different image size in case Strict
+mode is used.
+In case you want to suppress any non-error output, you can use Quiet mode by
+specifying @var{-q} option.
+
 @item convert [-c] [-p] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] 
[-o @var{options}] [-s @var{snapshot_name}] [-S @var{sparse_size}] 
@var{filename} address@hidden [...]] @var{output_filename}
 
 Convert the disk image @var{filename} or a snapshot @var{snapshot_name} to 
disk image @var{output_filename}