]> git.proxmox.com Git - mirror_qemu.git/blobdiff - qemu-img.c
Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging
[mirror_qemu.git] / qemu-img.c
index 25288c4d18d34ff1d95474ad1b246fffc8ccddf0..79983772de39e3e2b9f0d425a4043f28f0990716 100644 (file)
@@ -25,6 +25,7 @@
 #include "qemu/osdep.h"
 #include <getopt.h>
 
+#include "qemu-common.h"
 #include "qemu-version.h"
 #include "qapi/error.h"
 #include "qapi/qapi-visit-block-core.h"
@@ -37,6 +38,8 @@
 #include "qemu/option.h"
 #include "qemu/error-report.h"
 #include "qemu/log.h"
+#include "qemu/module.h"
+#include "qemu/units.h"
 #include "qom/object_interfaces.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/block-backend.h"
@@ -66,6 +69,7 @@ enum {
     OPTION_SIZE = 264,
     OPTION_PREALLOCATION = 265,
     OPTION_SHRINK = 266,
+    OPTION_SALVAGE = 267,
 };
 
 typedef enum OutputFormat {
@@ -85,13 +89,11 @@ static void QEMU_NORETURN GCC_FMT_ATTR(1, 2) error_exit(const char *fmt, ...)
 {
     va_list ap;
 
-    error_printf("qemu-img: ");
-
     va_start(ap, fmt);
-    error_vprintf(fmt, ap);
+    error_vreport(fmt, ap);
     va_end(ap);
 
-    error_printf("\nTry 'qemu-img --help' for more information\n");
+    error_printf("Try 'qemu-img --help' for more information\n");
     exit(EXIT_FAILURE);
 }
 
@@ -198,7 +200,7 @@ static void QEMU_NORETURN help(void)
            "  'skip=N' skip N bs-sized blocks at the start of input\n";
 
     printf("%s\nSupported formats:", help_msg);
-    bdrv_iterate_format(format_print, NULL);
+    bdrv_iterate_format(format_print, NULL, false);
     printf("\n\n" QEMU_HELP_BOTTOM "\n");
     exit(EXIT_SUCCESS);
 }
@@ -269,9 +271,20 @@ static int print_block_option_help(const char *filename, const char *fmt)
         create_opts = qemu_opts_append(create_opts, proto_drv->create_opts);
     }
 
-    printf("Supported options:\n");
+    if (filename) {
+        printf("Supported options:\n");
+    } else {
+        printf("Supported %s options:\n", fmt);
+    }
     qemu_opts_print_help(create_opts, false);
     qemu_opts_free(create_opts);
+
+    if (!filename) {
+        printf("\n"
+               "The protocol level may support further options.\n"
+               "Specify the target filename to include those options.\n");
+    }
+
     return 0;
 }
 
@@ -503,7 +516,7 @@ static int img_create(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         goto fail;
     }
 
@@ -753,7 +766,7 @@ static int img_check(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         return 1;
     }
 
@@ -966,7 +979,7 @@ static int img_commit(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         return 1;
     }
 
@@ -1207,7 +1220,7 @@ static int compare_buffers(const uint8_t *buf1, const uint8_t *buf2,
     return res;
 }
 
-#define IO_BUF_SIZE (2 * 1024 * 1024)
+#define IO_BUF_SIZE (2 * MiB)
 
 /*
  * Check if passed sectors are empty (not allocated or contain only 0 bytes)
@@ -1349,7 +1362,7 @@ static int img_compare(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         ret = 2;
         goto out4;
     }
@@ -1569,6 +1582,8 @@ typedef struct ImgConvertState {
     int64_t target_backing_sectors; /* negative if unknown */
     bool wr_in_order;
     bool copy_range;
+    bool salvage;
+    bool quiet;
     int min_sparse;
     int alignment;
     size_t cluster_sectors;
@@ -1615,23 +1630,44 @@ static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num)
     }
 
     if (s->sector_next_status <= sector_num) {
-        int64_t count = n * BDRV_SECTOR_SIZE;
+        uint64_t offset = (sector_num - src_cur_offset) * BDRV_SECTOR_SIZE;
+        int64_t count;
 
-        if (s->target_has_backing) {
+        do {
+            count = n * BDRV_SECTOR_SIZE;
+
+            if (s->target_has_backing) {
+                ret = bdrv_block_status(blk_bs(s->src[src_cur]), offset,
+                                        count, &count, NULL, NULL);
+            } else {
+                ret = bdrv_block_status_above(blk_bs(s->src[src_cur]), NULL,
+                                              offset, count, &count, NULL,
+                                              NULL);
+            }
+
+            if (ret < 0) {
+                if (s->salvage) {
+                    if (n == 1) {
+                        if (!s->quiet) {
+                            warn_report("error while reading block status at "
+                                        "offset %" PRIu64 ": %s", offset,
+                                        strerror(-ret));
+                        }
+                        /* Just try to read the data, then */
+                        ret = BDRV_BLOCK_DATA;
+                        count = BDRV_SECTOR_SIZE;
+                    } else {
+                        /* Retry on a shorter range */
+                        n = DIV_ROUND_UP(n, 4);
+                    }
+                } else {
+                    error_report("error while reading block status at offset "
+                                 "%" PRIu64 ": %s", offset, strerror(-ret));
+                    return ret;
+                }
+            }
+        } while (ret < 0);
 
-            ret = bdrv_block_status(blk_bs(s->src[src_cur]),
-                                    (sector_num - src_cur_offset) *
-                                    BDRV_SECTOR_SIZE,
-                                    count, &count, NULL, NULL);
-        } else {
-            ret = bdrv_block_status_above(blk_bs(s->src[src_cur]), NULL,
-                                          (sector_num - src_cur_offset) *
-                                          BDRV_SECTOR_SIZE,
-                                          count, &count, NULL, NULL);
-        }
-        if (ret < 0) {
-            return ret;
-        }
         n = DIV_ROUND_UP(count, BDRV_SECTOR_SIZE);
 
         if (ret & BDRV_BLOCK_ZERO) {
@@ -1668,15 +1704,15 @@ static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num)
 static int coroutine_fn convert_co_read(ImgConvertState *s, int64_t sector_num,
                                         int nb_sectors, uint8_t *buf)
 {
+    uint64_t single_read_until = 0;
     int n, ret;
-    QEMUIOVector qiov;
-    struct iovec iov;
 
     assert(nb_sectors <= s->buf_sectors);
     while (nb_sectors > 0) {
         BlockBackend *blk;
         int src_cur;
         int64_t bs_sectors, src_cur_offset;
+        uint64_t offset;
 
         /* In the case of compression with multiple source files, we can get a
          * nb_sectors that spreads into the next part. So we must be able to
@@ -1685,16 +1721,29 @@ static int coroutine_fn convert_co_read(ImgConvertState *s, int64_t sector_num,
         blk = s->src[src_cur];
         bs_sectors = s->src_sectors[src_cur];
 
+        offset = (sector_num - src_cur_offset) << BDRV_SECTOR_BITS;
+
         n = MIN(nb_sectors, bs_sectors - (sector_num - src_cur_offset));
-        iov.iov_base = buf;
-        iov.iov_len = n << BDRV_SECTOR_BITS;
-        qemu_iovec_init_external(&qiov, &iov, 1);
+        if (single_read_until > offset) {
+            n = 1;
+        }
 
-        ret = blk_co_preadv(
-                blk, (sector_num - src_cur_offset) << BDRV_SECTOR_BITS,
-                n << BDRV_SECTOR_BITS, &qiov, 0);
+        ret = blk_co_pread(blk, offset, n << BDRV_SECTOR_BITS, buf, 0);
         if (ret < 0) {
-            return ret;
+            if (s->salvage) {
+                if (n > 1) {
+                    single_read_until = offset + (n << BDRV_SECTOR_BITS);
+                    continue;
+                } else {
+                    if (!s->quiet) {
+                        warn_report("error while reading offset %" PRIu64
+                                    ": %s", offset, strerror(-ret));
+                    }
+                    memset(buf, 0, BDRV_SECTOR_SIZE);
+                }
+            } else {
+                return ret;
+            }
         }
 
         sector_num += n;
@@ -1711,8 +1760,6 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num,
                                          enum ImgConvertBlockStatus status)
 {
     int ret;
-    QEMUIOVector qiov;
-    struct iovec iov;
 
     while (nb_sectors > 0) {
         int n = nb_sectors;
@@ -1740,12 +1787,8 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num,
                 (s->compressed &&
                  !buffer_is_zero(buf, n * BDRV_SECTOR_SIZE)))
             {
-                iov.iov_base = buf;
-                iov.iov_len = n << BDRV_SECTOR_BITS;
-                qemu_iovec_init_external(&qiov, &iov, 1);
-
-                ret = blk_co_pwritev(s->target, sector_num << BDRV_SECTOR_BITS,
-                                     n << BDRV_SECTOR_BITS, &qiov, flags);
+                ret = blk_co_pwrite(s->target, sector_num << BDRV_SECTOR_BITS,
+                                    n << BDRV_SECTOR_BITS, buf, flags);
                 if (ret < 0) {
                     return ret;
                 }
@@ -1760,7 +1803,8 @@ static int coroutine_fn convert_co_write(ImgConvertState *s, int64_t sector_num,
             }
             ret = blk_co_pwrite_zeroes(s->target,
                                        sector_num << BDRV_SECTOR_BITS,
-                                       n << BDRV_SECTOR_BITS, 0);
+                                       n << BDRV_SECTOR_BITS,
+                                       BDRV_REQ_MAY_UNMAP);
             if (ret < 0) {
                 return ret;
             }
@@ -1938,7 +1982,7 @@ static int convert_do_copy(ImgConvertState *s)
     if (!s->has_zero_init && !s->target_has_backing &&
         bdrv_can_write_zeroes_with_unmap(blk_bs(s->target)))
     {
-        ret = blk_make_zero(s->target, BDRV_REQ_MAY_UNMAP);
+        ret = blk_make_zero(s->target, BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK);
         if (ret == 0) {
             s->has_zero_init = true;
         }
@@ -2008,7 +2052,7 @@ static int img_convert(int argc, char **argv)
     QDict *open_opts = NULL;
     char *options = NULL;
     Error *local_err = NULL;
-    bool writethrough, src_writethrough, quiet = false, image_opts = false,
+    bool writethrough, src_writethrough, image_opts = false,
          skip_create = false, progress = false, tgt_image_opts = false;
     int64_t ret = -EINVAL;
     bool force_share = false;
@@ -2030,6 +2074,7 @@ static int img_convert(int argc, char **argv)
             {"image-opts", no_argument, 0, OPTION_IMAGE_OPTS},
             {"force-share", no_argument, 0, 'U'},
             {"target-image-opts", no_argument, 0, OPTION_TARGET_IMAGE_OPTS},
+            {"salvage", no_argument, 0, OPTION_SALVAGE},
             {0, 0, 0, 0}
         };
         c = getopt_long(argc, argv, ":hf:O:B:Cco:l:S:pt:T:qnm:WU",
@@ -2116,7 +2161,7 @@ static int img_convert(int argc, char **argv)
             src_cache = optarg;
             break;
         case 'q':
-            quiet = true;
+            s.quiet = true;
             break;
         case 'n':
             skip_create = true;
@@ -2147,6 +2192,9 @@ static int img_convert(int argc, char **argv)
         case OPTION_IMAGE_OPTS:
             image_opts = true;
             break;
+        case OPTION_SALVAGE:
+            s.salvage = true;
+            break;
         case OPTION_TARGET_IMAGE_OPTS:
             tgt_image_opts = true;
             break;
@@ -2159,7 +2207,7 @@ static int img_convert(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         goto fail_getopt;
     }
 
@@ -2173,6 +2221,11 @@ static int img_convert(int argc, char **argv)
         goto fail_getopt;
     }
 
+    if (s.copy_range && s.salvage) {
+        error_report("Cannot use copy offloading in salvaging mode");
+        goto fail_getopt;
+    }
+
     if (tgt_image_opts && !skip_create) {
         error_report("--target-image-opts requires use of -n flag");
         goto fail_getopt;
@@ -2205,7 +2258,7 @@ static int img_convert(int argc, char **argv)
     }
 
     /* Initialize before goto out */
-    if (quiet) {
+    if (s.quiet) {
         progress = false;
     }
     qemu_progress_init(progress, 1.0);
@@ -2216,7 +2269,7 @@ static int img_convert(int argc, char **argv)
 
     for (bs_i = 0; bs_i < s.src_num; bs_i++) {
         s.src[bs_i] = img_open(image_opts, argv[optind + bs_i],
-                               fmt, src_flags, src_writethrough, quiet,
+                               fmt, src_flags, src_writethrough, s.quiet,
                                force_share);
         if (!s.src[bs_i]) {
             ret = -1;
@@ -2379,7 +2432,7 @@ static int img_convert(int argc, char **argv)
 
     if (skip_create) {
         s.target = img_open(tgt_image_opts, out_filename, out_fmt,
-                            flags, writethrough, quiet, false);
+                            flags, writethrough, s.quiet, false);
     } else {
         /* TODO ultimately we should allow --target-image-opts
          * to be used even when -n is not given.
@@ -2387,7 +2440,7 @@ static int img_convert(int argc, char **argv)
          * to allow filenames in option syntax
          */
         s.target = img_open_file(out_filename, open_opts, out_fmt,
-                                 flags, writethrough, quiet, false);
+                                 flags, writethrough, s.quiet, false);
         open_opts = NULL; /* blk_new_open will have freed it */
     }
     if (!s.target) {
@@ -2488,11 +2541,11 @@ static void dump_snapshots(BlockDriverState *bs)
     if (nb_sns <= 0)
         return;
     printf("Snapshot list:\n");
-    bdrv_snapshot_dump(fprintf, stdout, NULL);
+    bdrv_snapshot_dump(NULL);
     printf("\n");
     for(i = 0; i < nb_sns; i++) {
         sn = &sn_tab[i];
-        bdrv_snapshot_dump(fprintf, stdout, sn);
+        bdrv_snapshot_dump(sn);
         printf("\n");
     }
     g_free(sn_tab);
@@ -2541,7 +2594,7 @@ static void dump_human_image_info_list(ImageInfoList *list)
         }
         delim = true;
 
-        bdrv_image_info_dump(fprintf, stdout, elem->value);
+        bdrv_image_info_dump(elem->value);
     }
 }
 
@@ -2713,7 +2766,7 @@ static int img_info(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         return 1;
     }
 
@@ -2740,14 +2793,14 @@ static int img_info(int argc, char **argv)
     return 0;
 }
 
-static void dump_map_entry(OutputFormat output_format, MapEntry *e,
-                           MapEntry *next)
+static int dump_map_entry(OutputFormat output_format, MapEntry *e,
+                          MapEntry *next)
 {
     switch (output_format) {
     case OFORMAT_HUMAN:
         if (e->data && !e->has_offset) {
             error_report("File contains external, encrypted or compressed clusters.");
-            exit(1);
+            return -1;
         }
         if (e->data && !e->zero) {
             printf("%#-16"PRIx64"%#-16"PRIx64"%#-16"PRIx64"%s\n",
@@ -2780,6 +2833,7 @@ static void dump_map_entry(OutputFormat output_format, MapEntry *e,
         }
         break;
     }
+    return 0;
 }
 
 static int get_block_status(BlockDriverState *bs, int64_t offset,
@@ -2790,6 +2844,7 @@ static int get_block_status(BlockDriverState *bs, int64_t offset,
     BlockDriverState *file;
     bool has_offset;
     int64_t map;
+    char *filename = NULL;
 
     /* As an optimization, we could cache the current range of unallocated
      * clusters in each file of the chain, and avoid querying the same
@@ -2817,6 +2872,11 @@ static int get_block_status(BlockDriverState *bs, int64_t offset,
 
     has_offset = !!(ret & BDRV_BLOCK_OFFSET_VALID);
 
+    if (file && has_offset) {
+        bdrv_refresh_filename(file);
+        filename = file->filename;
+    }
+
     *e = (MapEntry) {
         .start = offset,
         .length = bytes,
@@ -2825,8 +2885,8 @@ static int get_block_status(BlockDriverState *bs, int64_t offset,
         .offset = map,
         .has_offset = has_offset,
         .depth = depth,
-        .has_filename = file && has_offset,
-        .filename = file && has_offset ? file->filename : NULL,
+        .has_filename = filename,
+        .filename = filename,
     };
 
     return 0;
@@ -2932,7 +2992,7 @@ static int img_map(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         return 1;
     }
 
@@ -2952,7 +3012,7 @@ static int img_map(int argc, char **argv)
         int64_t n;
 
         /* Probe up to 1 GiB at a time.  */
-        n = MIN(1 << 30, length - offset);
+        n = MIN(1 * GiB, length - offset);
         ret = get_block_status(bs, offset, n, &next);
 
         if (ret < 0) {
@@ -2966,12 +3026,15 @@ static int img_map(int argc, char **argv)
         }
 
         if (curr.length > 0) {
-            dump_map_entry(output_format, &curr, &next);
+            ret = dump_map_entry(output_format, &curr, &next);
+            if (ret < 0) {
+                goto out;
+            }
         }
         curr = next;
     }
 
-    dump_map_entry(output_format, &curr, NULL);
+    ret = dump_map_entry(output_format, &curr, NULL);
 
 out:
     blk_unref(blk);
@@ -3081,7 +3144,7 @@ static int img_snapshot(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         return 1;
     }
 
@@ -3123,11 +3186,18 @@ static int img_snapshot(int argc, char **argv)
         break;
 
     case SNAPSHOT_DELETE:
-        bdrv_snapshot_delete_by_id_or_name(bs, snapshot_name, &err);
-        if (err) {
-            error_reportf_err(err, "Could not delete snapshot '%s': ",
-                              snapshot_name);
+        ret = bdrv_snapshot_find(bs, &sn, snapshot_name);
+        if (ret < 0) {
+            error_report("Could not delete snapshot '%s': snapshot not "
+                         "found", snapshot_name);
             ret = 1;
+        } else {
+            ret = bdrv_snapshot_delete(bs, sn.id_str, sn.name, &err);
+            if (ret < 0) {
+                error_reportf_err(err, "Could not delete snapshot '%s': ",
+                                  snapshot_name);
+                ret = 1;
+            }
         }
         break;
     }
@@ -3145,7 +3215,7 @@ static int img_rebase(int argc, char **argv)
     BlockBackend *blk = NULL, *blk_old_backing = NULL, *blk_new_backing = NULL;
     uint8_t *buf_old = NULL;
     uint8_t *buf_new = NULL;
-    BlockDriverState *bs = NULL;
+    BlockDriverState *bs = NULL, *prefix_chain_bs = NULL;
     char *filename;
     const char *fmt, *cache, *src_cache, *out_basefmt, *out_baseimg;
     int c, flags, src_flags, ret;
@@ -3241,7 +3311,7 @@ static int img_rebase(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         return 1;
     }
 
@@ -3290,29 +3360,23 @@ static int img_rebase(int argc, char **argv)
 
     /* For safe rebasing we need to compare old and new backing file */
     if (!unsafe) {
-        char backing_name[PATH_MAX];
         QDict *options = NULL;
-
-        if (bs->backing_format[0] != '\0') {
-            options = qdict_new();
-            qdict_put_str(options, "driver", bs->backing_format);
-        }
-
-        if (force_share) {
-            if (!options) {
-                options = qdict_new();
+        BlockDriverState *base_bs = backing_bs(bs);
+
+        if (base_bs) {
+            blk_old_backing = blk_new(qemu_get_aio_context(),
+                                      BLK_PERM_CONSISTENT_READ,
+                                      BLK_PERM_ALL);
+            ret = blk_insert_bs(blk_old_backing, base_bs,
+                                &local_err);
+            if (ret < 0) {
+                error_reportf_err(local_err,
+                                  "Could not reuse old backing file '%s': ",
+                                  base_bs->filename);
+                goto out;
             }
-            qdict_put_bool(options, BDRV_OPT_FORCE_SHARE, true);
-        }
-        bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
-        blk_old_backing = blk_new_open(backing_name, NULL,
-                                       options, src_flags, &local_err);
-        if (!blk_old_backing) {
-            error_reportf_err(local_err,
-                              "Could not open old backing file '%s': ",
-                              backing_name);
-            ret = -1;
-            goto out;
+        } else {
+            blk_old_backing = NULL;
         }
 
         if (out_baseimg[0]) {
@@ -3327,32 +3391,52 @@ static int img_rebase(int argc, char **argv)
                 qdict_put_bool(options, BDRV_OPT_FORCE_SHARE, true);
             }
 
+            bdrv_refresh_filename(bs);
             overlay_filename = bs->exact_filename[0] ? bs->exact_filename
                                                      : bs->filename;
-            out_real_path = g_malloc(PATH_MAX);
-
-            bdrv_get_full_backing_filename_from_filename(overlay_filename,
-                                                         out_baseimg,
-                                                         out_real_path,
-                                                         PATH_MAX,
-                                                         &local_err);
+            out_real_path =
+                bdrv_get_full_backing_filename_from_filename(overlay_filename,
+                                                             out_baseimg,
+                                                             &local_err);
             if (local_err) {
+                qobject_unref(options);
                 error_reportf_err(local_err,
                                   "Could not resolve backing filename: ");
                 ret = -1;
-                g_free(out_real_path);
                 goto out;
             }
 
-            blk_new_backing = blk_new_open(out_real_path, NULL,
-                                           options, src_flags, &local_err);
-            g_free(out_real_path);
-            if (!blk_new_backing) {
-                error_reportf_err(local_err,
-                                  "Could not open new backing file '%s': ",
-                                  out_baseimg);
-                ret = -1;
-                goto out;
+            /*
+             * Find out whether we rebase an image on top of a previous image
+             * in its chain.
+             */
+            prefix_chain_bs = bdrv_find_backing_image(bs, out_real_path);
+            if (prefix_chain_bs) {
+                qobject_unref(options);
+                g_free(out_real_path);
+
+                blk_new_backing = blk_new(qemu_get_aio_context(),
+                                          BLK_PERM_CONSISTENT_READ,
+                                          BLK_PERM_ALL);
+                ret = blk_insert_bs(blk_new_backing, prefix_chain_bs,
+                                    &local_err);
+                if (ret < 0) {
+                    error_reportf_err(local_err,
+                                      "Could not reuse backing file '%s': ",
+                                      out_baseimg);
+                    goto out;
+                }
+            } else {
+                blk_new_backing = blk_new_open(out_real_path, NULL,
+                                               options, src_flags, &local_err);
+                g_free(out_real_path);
+                if (!blk_new_backing) {
+                    error_reportf_err(local_err,
+                                      "Could not open new backing file '%s': ",
+                                      out_baseimg);
+                    ret = -1;
+                    goto out;
+                }
             }
         }
     }
@@ -3368,7 +3452,7 @@ static int img_rebase(int argc, char **argv)
      */
     if (!unsafe) {
         int64_t size;
-        int64_t old_backing_size;
+        int64_t old_backing_size = 0;
         int64_t new_backing_size = 0;
         uint64_t offset;
         int64_t n;
@@ -3384,15 +3468,18 @@ static int img_rebase(int argc, char **argv)
             ret = -1;
             goto out;
         }
-        old_backing_size = blk_getlength(blk_old_backing);
-        if (old_backing_size < 0) {
-            char backing_name[PATH_MAX];
+        if (blk_old_backing) {
+            old_backing_size = blk_getlength(blk_old_backing);
+            if (old_backing_size < 0) {
+                char backing_name[PATH_MAX];
 
-            bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
-            error_report("Could not get size of '%s': %s",
-                         backing_name, strerror(-old_backing_size));
-            ret = -1;
-            goto out;
+                bdrv_get_backing_filename(bs, backing_name,
+                                          sizeof(backing_name));
+                error_report("Could not get size of '%s': %s",
+                             backing_name, strerror(-old_backing_size));
+                ret = -1;
+                goto out;
+            }
         }
         if (blk_new_backing) {
             new_backing_size = blk_getlength(blk_new_backing);
@@ -3409,6 +3496,8 @@ static int img_rebase(int argc, char **argv)
         }
 
         for (offset = 0; offset < size; offset += n) {
+            bool buf_old_is_zero = false;
+
             /* How many bytes can we handle with the next read? */
             n = MIN(IO_BUF_SIZE, size - offset);
 
@@ -3423,12 +3512,30 @@ static int img_rebase(int argc, char **argv)
                 continue;
             }
 
+            if (prefix_chain_bs) {
+                /*
+                 * If cluster wasn't changed since prefix_chain, we don't need
+                 * to take action
+                 */
+                ret = bdrv_is_allocated_above(backing_bs(bs), prefix_chain_bs,
+                                              false, offset, n, &n);
+                if (ret < 0) {
+                    error_report("error while reading image metadata: %s",
+                                 strerror(-ret));
+                    goto out;
+                }
+                if (!ret) {
+                    continue;
+                }
+            }
+
             /*
              * Read old and new backing file and take into consideration that
              * backing files may be smaller than the COW image.
              */
             if (offset >= old_backing_size) {
                 memset(buf_old, 0, n);
+                buf_old_is_zero = true;
             } else {
                 if (offset + n > old_backing_size) {
                     n = old_backing_size - offset;
@@ -3464,8 +3571,12 @@ static int img_rebase(int argc, char **argv)
                 if (compare_buffers(buf_old + written, buf_new + written,
                                     n - written, &pnum))
                 {
-                    ret = blk_pwrite(blk, offset + written,
-                                     buf_old + written, pnum, 0);
+                    if (buf_old_is_zero) {
+                        ret = blk_pwrite_zeroes(blk, offset + written, pnum, 0);
+                    } else {
+                        ret = blk_pwrite(blk, offset + written,
+                                         buf_old + written, pnum, 0);
+                    }
                     if (ret < 0) {
                         error_report("Error while writing to COW image: %s",
                             strerror(-ret));
@@ -3621,7 +3732,7 @@ static int img_resize(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         return 1;
     }
 
@@ -3865,7 +3976,7 @@ static int img_amend(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         ret = -1;
         goto out_no_progress;
     }
@@ -4509,7 +4620,7 @@ static int img_dd(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         ret = -1;
         goto out;
     }
@@ -4786,7 +4897,7 @@ static int img_measure(int argc, char **argv)
 
     if (qemu_opts_foreach(&qemu_object_opts,
                           user_creatable_add_opts_foreach,
-                          NULL, NULL)) {
+                          NULL, &error_fatal)) {
         goto out;
     }
 
@@ -4912,8 +5023,8 @@ int main(int argc, char **argv)
     signal(SIGPIPE, SIG_IGN);
 #endif
 
+    error_init(argv[0]);
     module_call_init(MODULE_INIT_TRACE);
-    error_set_progname(argv[0]);
     qemu_init_exec_dir(argv[0]);
 
     if (qemu_init_main_loop(&local_error)) {