[Qemu-devel] [PATCH] 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.

Signed-off-by: Reda Sallahi <fullmanet@gmail.com>
---
Depends on:
[PATCH v2] qemu-img: add conv=notrunc option to dd

 qemu-img.c | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 76 insertions(+), 15 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index 7c546c1..dfa0e63 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3919,6 +3919,8 @@ static int img_dd(int argc, char **argv)
     char *tmp;
     BlockDriver *drv = NULL, *proto_drv = NULL;
     BlockBackend *blk1 = NULL, *blk2 = NULL;
+    BlockDriverState *bs = NULL;
+    QDict *qoptions = NULL;
     QemuOpts *opts = NULL;
     QemuOptsList *create_opts = NULL;
     Error *local_err = NULL;
@@ -4080,22 +4082,60 @@ static int img_dd(int argc, char **argv)
         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);
-    } 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;
+    bs = bdrv_open(out.filename, NULL, qoptions, BDRV_O_RDWR, &local_err);
+
+    if (!bs) {
+        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,
@@ -4117,6 +4157,26 @@ static int img_dd(int argc, char **argv)
         in_pos = in.offset * in.bsz;
     }
 
+    if (bs) {
+        int64_t 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);
+            }
+        }
+    }
+
     in.buf = g_new(uint8_t, in.bsz);
 
     for (out_pos = 0; in_pos < size; block_count++) {
@@ -4152,6 +4212,7 @@ out:
     qemu_opts_free(create_opts);
     blk_unref(blk1);
     blk_unref(blk2);
+    bdrv_unref(bs);
     g_free(in.filename);
     g_free(out.filename);
     g_free(in.buf);
-- 
2.9.2