block: Generic file creation fallback
If a protocol driver does not support image creation, we can see whether
maybe the file exists already. If so, just truncating it will be
sufficient.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200122164532.178040-3-mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
diff --git a/block.c b/block.c
index 08372ce..308a91c 100644
--- a/block.c
+++ b/block.c
@@ -532,20 +532,139 @@
return ret;
}
+/**
+ * Helper function for bdrv_create_file_fallback(): Resize @blk to at
+ * least the given @minimum_size.
+ *
+ * On success, return @blk's actual length.
+ * Otherwise, return -errno.
+ */
+static int64_t create_file_fallback_truncate(BlockBackend *blk,
+ int64_t minimum_size, Error **errp)
+{
+ Error *local_err = NULL;
+ int64_t size;
+ int ret;
+
+ ret = blk_truncate(blk, minimum_size, false, PREALLOC_MODE_OFF, &local_err);
+ if (ret < 0 && ret != -ENOTSUP) {
+ error_propagate(errp, local_err);
+ return ret;
+ }
+
+ size = blk_getlength(blk);
+ if (size < 0) {
+ error_free(local_err);
+ error_setg_errno(errp, -size,
+ "Failed to inquire the new image file's length");
+ return size;
+ }
+
+ if (size < minimum_size) {
+ /* Need to grow the image, but we failed to do that */
+ error_propagate(errp, local_err);
+ return -ENOTSUP;
+ }
+
+ error_free(local_err);
+ local_err = NULL;
+
+ return size;
+}
+
+/**
+ * Helper function for bdrv_create_file_fallback(): Zero the first
+ * sector to remove any potentially pre-existing image header.
+ */
+static int create_file_fallback_zero_first_sector(BlockBackend *blk,
+ int64_t current_size,
+ Error **errp)
+{
+ int64_t bytes_to_clear;
+ int ret;
+
+ bytes_to_clear = MIN(current_size, BDRV_SECTOR_SIZE);
+ if (bytes_to_clear) {
+ ret = blk_pwrite_zeroes(blk, 0, bytes_to_clear, BDRV_REQ_MAY_UNMAP);
+ if (ret < 0) {
+ error_setg_errno(errp, -ret,
+ "Failed to clear the new image's first sector");
+ return ret;
+ }
+ }
+
+ return 0;
+}
+
+static int bdrv_create_file_fallback(const char *filename, BlockDriver *drv,
+ QemuOpts *opts, Error **errp)
+{
+ BlockBackend *blk;
+ QDict *options = qdict_new();
+ int64_t size = 0;
+ char *buf = NULL;
+ PreallocMode prealloc;
+ Error *local_err = NULL;
+ int ret;
+
+ size = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0);
+ buf = qemu_opt_get_del(opts, BLOCK_OPT_PREALLOC);
+ prealloc = qapi_enum_parse(&PreallocMode_lookup, buf,
+ PREALLOC_MODE_OFF, &local_err);
+ g_free(buf);
+ if (local_err) {
+ error_propagate(errp, local_err);
+ return -EINVAL;
+ }
+
+ if (prealloc != PREALLOC_MODE_OFF) {
+ error_setg(errp, "Unsupported preallocation mode '%s'",
+ PreallocMode_str(prealloc));
+ return -ENOTSUP;
+ }
+
+ qdict_put_str(options, "driver", drv->format_name);
+
+ blk = blk_new_open(filename, NULL, options,
+ BDRV_O_RDWR | BDRV_O_RESIZE, errp);
+ if (!blk) {
+ error_prepend(errp, "Protocol driver '%s' does not support image "
+ "creation, and opening the image failed: ",
+ drv->format_name);
+ return -EINVAL;
+ }
+
+ size = create_file_fallback_truncate(blk, size, errp);
+ if (size < 0) {
+ ret = size;
+ goto out;
+ }
+
+ ret = create_file_fallback_zero_first_sector(blk, size, errp);
+ if (ret < 0) {
+ goto out;
+ }
+
+ ret = 0;
+out:
+ blk_unref(blk);
+ return ret;
+}
+
int bdrv_create_file(const char *filename, QemuOpts *opts, Error **errp)
{
BlockDriver *drv;
- Error *local_err = NULL;
- int ret;
drv = bdrv_find_protocol(filename, true, errp);
if (drv == NULL) {
return -ENOENT;
}
- ret = bdrv_create(drv, filename, opts, &local_err);
- error_propagate(errp, local_err);
- return ret;
+ if (drv->bdrv_co_create_opts) {
+ return bdrv_create(drv, filename, opts, errp);
+ } else {
+ return bdrv_create_file_fallback(filename, drv, opts, errp);
+ }
}
/**
@@ -1444,6 +1563,24 @@
},
};
+static QemuOptsList fallback_create_opts = {
+ .name = "fallback-create-opts",
+ .head = QTAILQ_HEAD_INITIALIZER(fallback_create_opts.head),
+ .desc = {
+ {
+ .name = BLOCK_OPT_SIZE,
+ .type = QEMU_OPT_SIZE,
+ .help = "Virtual disk size"
+ },
+ {
+ .name = BLOCK_OPT_PREALLOC,
+ .type = QEMU_OPT_STRING,
+ .help = "Preallocation mode (allowed values: off)"
+ },
+ { /* end of list */ }
+ }
+};
+
/*
* Common part for opening disk images and files
*
@@ -5772,15 +5909,13 @@
return;
}
- if (!proto_drv->create_opts) {
- error_setg(errp, "Protocol driver '%s' does not support image creation",
- proto_drv->format_name);
- return;
- }
-
/* Create parameter list */
create_opts = qemu_opts_append(create_opts, drv->create_opts);
- create_opts = qemu_opts_append(create_opts, proto_drv->create_opts);
+ if (proto_drv->create_opts) {
+ create_opts = qemu_opts_append(create_opts, proto_drv->create_opts);
+ } else {
+ create_opts = qemu_opts_append(create_opts, &fallback_create_opts);
+ }
opts = qemu_opts_create(create_opts, NULL, 0, &error_abort);
