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block: Allow omitting the file name when using driver-specific options

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After this patch, using -drive with an empty file name continues to open
the file if driver-specific options are used. If no driver-specific
options are specified, the semantics stay as it was: It defines a drive
without an inserted medium.

In order to achieve this, bdrv_open() must be made safe to work with a
NULL filename parameter. The assumption that is made is that only block
drivers which implement bdrv_parse_filename() support using driver
specific options and could therefore work without a filename. These
drivers must make sure to cope with NULL in their implementation of
.bdrv_open() (this is only NBD for now). For all other drivers, the
block layer code will make sure to error out before calling into their
code - they can't possibly work without a filename.

Now an NBD connection can be opened like this:

  qemu-system-x86_64 -drive file.driver=nbd,file.port=1234,file.host=::1

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Kevin Wolf 2013-03-18 16:40:51 +01:00
parent f5866fa438
commit c2ad1b0c46
3 changed files with 51 additions and 11 deletions
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10
blockdev.c
View file

@ -658,7 +658,11 @@ DriveInfo *drive_init(QemuOpts *all_opts, BlockInterfaceType block_default_type)
abort();
}
if (!file || !*file) {
return dinfo;
if (qdict_size(bs_opts)) {
file = NULL;
} else {
return dinfo;
}
}
if (snapshot) {
/* always use cache=unsafe with snapshot */
@ -697,10 +701,10 @@ DriveInfo *drive_init(QemuOpts *all_opts, BlockInterfaceType block_default_type)
if (ret < 0) {
if (ret == -EMEDIUMTYPE) {
error_report("could not open disk image %s: not in %s format",
file, drv->format_name);
file ?: dinfo->id, drv->format_name);
} else {
error_report("could not open disk image %s: %s",
file, strerror(-ret));
file ?: dinfo->id, strerror(-ret));
}
goto err;
}