[Qemu-devel] [PATCH v3] qemu-img: change opening method for the output in dd

[Reda Sallahi <fullmanet@gmail.com>]

dd was creating an output image regardless of whether there was one already
created. With this patch we try to open first the output image and resize it
if necessary.

We also make it mandatory to specify conv=notrunc when the file already
exists.

Signed-off-by: Reda Sallahi <fullmanet@gmail.com>
---
Depends on:
[PATCH v3] qemu-img: add conv=notrunc option to dd

Changes from v2:
* Remove redundant code
Changes from v1:
* add --image-opts handling

 qemu-img.c | 149 ++++++++++++++++++++++++++++++++++++++++---------------------
 1 file changed, 98 insertions(+), 51 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index d08905b..8af6dd9 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3919,7 +3919,8 @@ static int img_dd(int argc, char **argv)
     char *tmp;
     BlockDriver *drv = NULL, *proto_drv = NULL;
     BlockBackend *blk1 = NULL, *blk2 = NULL;
-    QemuOpts *opts = NULL;
+    QDict *qoptions = NULL;
+    QemuOpts *opts = NULL, *qopts = NULL;
     QemuOptsList *create_opts = NULL;
     Error *local_err = NULL;
     bool image_opts = false;
@@ -4030,36 +4031,6 @@ static int img_dd(int argc, char **argv)
         goto out;
     }
 
-    drv = bdrv_find_format(out_fmt);
-    if (!drv) {
-        error_report("Unknown file format");
-        ret = -1;
-        goto out;
-    }
-    proto_drv = bdrv_find_protocol(out.filename, true, &local_err);
-
-    if (!proto_drv) {
-        error_report_err(local_err);
-        ret = -1;
-        goto out;
-    }
-    if (!drv->create_opts) {
-        error_report("Format driver '%s' does not support image creation",
-                     drv->format_name);
-        ret = -1;
-        goto out;
-    }
-    if (!proto_drv->create_opts) {
-        error_report("Protocol driver '%s' does not support image creation",
-                     proto_drv->format_name);
-        ret = -1;
-        goto out;
-    }
-    create_opts = qemu_opts_append(create_opts, drv->create_opts);
-    create_opts = qemu_opts_append(create_opts, proto_drv->create_opts);
-
-    opts = qemu_opts_create(create_opts, NULL, 0, &error_abort);
-
     size = blk_getlength(blk1);
     if (size < 0) {
         error_report("Failed to get size for '%s'", in.filename);
@@ -4071,31 +4042,106 @@ static int img_dd(int argc, char **argv)
         dd.count * in.bsz < size) {
         size = dd.count * in.bsz;
     }
-
-    /* Overflow means the specified offset is beyond input image's size */
-    if (dd.flags & C_SKIP && (in.offset > INT64_MAX / in.bsz ||
-                              size < in.bsz * in.offset)) {
-        qemu_opt_set_number(opts, BLOCK_OPT_SIZE, 0, &error_abort);
+    if (image_opts) {
+        qopts = qemu_opts_parse_noisily(qemu_find_opts("source"),
+                                        out.filename, true);
+        if (!opts) {
+            ret = -1;
+            goto out;
+        }
+        qoptions = qemu_opts_to_qdict(qopts, NULL);
     } else {
-        qemu_opt_set_number(opts, BLOCK_OPT_SIZE,
-                            size - in.bsz * in.offset, &error_abort);
+        qoptions = qdict_new();
+        qdict_put(qoptions, "driver", qstring_from_str(out_fmt));
     }
 
-    ret = bdrv_create(drv, out.filename, opts, &local_err);
-    if (ret < 0) {
-        error_reportf_err(local_err,
-                          "%s: error while creating output image: ",
-                          out.filename);
-        ret = -1;
-        goto out;
-    }
-
-    blk2 = img_open(image_opts, out.filename, out_fmt, BDRV_O_RDWR,
-                    false, false);
+    blk2 = blk_new_open(image_opts ? NULL : out.filename,
+                        NULL, qoptions, BDRV_O_RDWR, NULL);
 
     if (!blk2) {
-        ret = -1;
-        goto out;
+        drv = bdrv_find_format(out_fmt);
+        if (!drv) {
+            error_report("Unknown file format");
+            ret = -1;
+            goto out;
+        }
+        proto_drv = bdrv_find_protocol(out.filename, true, &local_err);
+
+        if (!proto_drv) {
+            error_report_err(local_err);
+            ret = -1;
+            goto out;
+        }
+        if (!drv->create_opts) {
+            error_report("Format driver '%s' does not support image creation",
+                         drv->format_name);
+            ret = -1;
+            goto out;
+        }
+        if (!proto_drv->create_opts) {
+            error_report("Protocol driver '%s' does not support image creation",
+                         proto_drv->format_name);
+            ret = -1;
+            goto out;
+        }
+        create_opts = qemu_opts_append(create_opts, drv->create_opts);
+        create_opts = qemu_opts_append(create_opts, proto_drv->create_opts);
+
+        opts = qemu_opts_create(create_opts, NULL, 0, &error_abort);
+
+        /* Overflow means the specified offset is beyond input image's size */
+        if (dd.flags & C_SKIP && (in.offset > INT64_MAX / in.bsz ||
+                                  size < in.offset * in.bsz)) {
+            qemu_opt_set_number(opts, BLOCK_OPT_SIZE,
+                                0, &error_abort);
+        } else {
+            qemu_opt_set_number(opts, BLOCK_OPT_SIZE,
+                                size - in.offset * in.bsz, &error_abort);
+        }
+
+        ret = bdrv_create(drv, out.filename, opts, &local_err);
+        if (ret < 0) {
+            error_reportf_err(local_err,
+                              "%s: error while creating output image: ",
+                              out.filename);
+            ret = -1;
+            goto out;
+        }
+        blk2 = img_open(image_opts, out.filename, out_fmt, BDRV_O_RDWR,
+                        false, false);
+        if (!blk2) {
+            ret = -1;
+            goto out;
+        }
+    } else {
+        int64_t blk2sz = 0;
+
+        if (!(dd.conv & C_NOTRUNC)) {
+            /* We make conv=notrunc mandatory for the moment to avoid
+               accidental destruction of the output image. Needs to be
+               changed when a better solution is found */
+            error_report("conv=notrunc not specified");
+            ret = -1;
+            goto out;
+        }
+
+        blk2sz = blk_getlength(blk2);
+        if (blk2sz < 0) {
+            error_report("Failed to get size for '%s'", in.filename);
+            ret = -1;
+            goto out;
+        }
+
+        if (!(dd.conv & C_NOTRUNC)) {
+            blk_truncate(blk2, 0);
+        }
+        if (!(dd.flags & C_SKIP) || (in.offset <= INT64_MAX / in.bsz &&
+                                     size >= in.offset * in.bsz)) {
+            if (!(dd.conv & C_NOTRUNC) ||
+                blk2sz < size - in.offset * in.bsz) {
+                blk_truncate(blk2, size - in.offset * in.bsz);
+            }
+        }
     }
 
     if (dd.flags & C_SKIP && (in.offset > INT64_MAX / in.bsz ||
@@ -4141,6 +4187,7 @@ static int img_dd(int argc, char **argv)
 out:
     g_free(arg);
     qemu_opts_del(opts);
+    qemu_opts_del(qopts);
     qemu_opts_free(create_opts);
     blk_unref(blk1);
     blk_unref(blk2);
-- 
2.9.3