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>
This commit is contained in:
Max Reitz 2020-01-22 17:45:29 +01:00
parent 78c81a3f10
commit fd17146cd9

157
block.c
View File

@ -532,20 +532,139 @@ out:
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 @@ QemuOptsList bdrv_runtime_opts = {
},
};
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 @@ void bdrv_img_create(const char *filename, const char *fmt,
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);
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);