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block: Add bdrv_refresh_filename() 

Some block devices may not have a filename in their BDS; and for some,
there may not even be a normal filename at all. To work around this, add
a function which tries to construct a valid filename for the
BDS.filename field.

If a filename exists or a block driver is able to reconstruct a valid
filename (which is placed in BDS.exact_filename), this can directly be
used.

If no filename can be constructed, we can still construct an options
QDict which is then converted to a JSON object and prefixed with the
"json:" pseudo protocol prefix. The QDict is placed in
BDS.full_open_options.

For most block drivers, this process can be done automatically; those
that need special handling may define a .bdrv_refresh_filename() method
to fill BDS.exact_filename and BDS.full_open_options themselves.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2014-07-18 20:24:56 +02:00 committed by Kevin Wolf
parent 1bdb176ac5
commit 91af701412
3 changed files with 142 additions and 0 deletions
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135
block.c
View File

@ -964,6 +964,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
} else {
bs->filename[0] = '\0';
}
pstrcpy(bs->exact_filename, sizeof(bs->exact_filename), bs->filename);
bs->drv = drv;
bs->opaque = g_malloc0(drv->instance_size);
@ -1505,6 +1506,8 @@ int bdrv_open(BlockDriverState **pbs, const char *filename,
}
}
bdrv_refresh_filename(bs);
/* For snapshot=on, create a temporary qcow2 overlay. bs points to the
* temporary snapshot afterwards. */
if (snapshot_flags) {
@ -1845,6 +1848,8 @@ void bdrv_close(BlockDriverState *bs)
bs->zero_beyond_eof = false;
QDECREF(bs->options);
bs->options = NULL;
QDECREF(bs->full_open_options);
bs->full_open_options = NULL;
if (bs->file != NULL) {
bdrv_unref(bs->file);
@ -5894,3 +5899,133 @@ void bdrv_flush_io_queue(BlockDriverState *bs)
bdrv_flush_io_queue(bs->file);
}
}
static bool append_open_options(QDict *d, BlockDriverState *bs)
{
const QDictEntry *entry;
bool found_any = false;
for (entry = qdict_first(bs->options); entry;
entry = qdict_next(bs->options, entry))
{
/* Only take options for this level and exclude all non-driver-specific
* options */
if (!strchr(qdict_entry_key(entry), '.') &&
strcmp(qdict_entry_key(entry), "node-name"))
{
qobject_incref(qdict_entry_value(entry));
qdict_put_obj(d, qdict_entry_key(entry), qdict_entry_value(entry));
found_any = true;
}
}
return found_any;
}
/* Updates the following BDS fields:
* - exact_filename: A filename which may be used for opening a block device
* which (mostly) equals the given BDS (even without any
* other options; so reading and writing must return the same
* results, but caching etc. may be different)
* - full_open_options: Options which, when given when opening a block device
* (without a filename), result in a BDS (mostly)
* equalling the given one
* - filename: If exact_filename is set, it is copied here. Otherwise,
* full_open_options is converted to a JSON object, prefixed with
* "json:" (for use through the JSON pseudo protocol) and put here.
*/
void bdrv_refresh_filename(BlockDriverState *bs)
{
BlockDriver *drv = bs->drv;
QDict *opts;
if (!drv) {
return;
}
/* This BDS's file name will most probably depend on its file's name, so
* refresh that first */
if (bs->file) {
bdrv_refresh_filename(bs->file);
}
if (drv->bdrv_refresh_filename) {
/* Obsolete information is of no use here, so drop the old file name
* information before refreshing it */
bs->exact_filename[0] = '\0';
if (bs->full_open_options) {
QDECREF(bs->full_open_options);
bs->full_open_options = NULL;
}
drv->bdrv_refresh_filename(bs);
} else if (bs->file) {
/* Try to reconstruct valid information from the underlying file */
bool has_open_options;
bs->exact_filename[0] = '\0';
if (bs->full_open_options) {
QDECREF(bs->full_open_options);
bs->full_open_options = NULL;
}
opts = qdict_new();
has_open_options = append_open_options(opts, bs);
/* If no specific options have been given for this BDS, the filename of
* the underlying file should suffice for this one as well */
if (bs->file->exact_filename[0] && !has_open_options) {
strcpy(bs->exact_filename, bs->file->exact_filename);
}
/* Reconstructing the full options QDict is simple for most format block
* drivers, as long as the full options are known for the underlying
* file BDS. The full options QDict of that file BDS should somehow
* contain a representation of the filename, therefore the following
* suffices without querying the (exact_)filename of this BDS. */
if (bs->file->full_open_options) {
qdict_put_obj(opts, "driver",
QOBJECT(qstring_from_str(drv->format_name)));
QINCREF(bs->file->full_open_options);
qdict_put_obj(opts, "file", QOBJECT(bs->file->full_open_options));
bs->full_open_options = opts;
} else {
QDECREF(opts);
}
} else if (!bs->full_open_options && qdict_size(bs->options)) {
/* There is no underlying file BDS (at least referenced by BDS.file),
* so the full options QDict should be equal to the options given
* specifically for this block device when it was opened (plus the
* driver specification).
* Because those options don't change, there is no need to update
* full_open_options when it's already set. */
opts = qdict_new();
append_open_options(opts, bs);
qdict_put_obj(opts, "driver",
QOBJECT(qstring_from_str(drv->format_name)));
if (bs->exact_filename[0]) {
/* This may not work for all block protocol drivers (some may
* require this filename to be parsed), but we have to find some
* default solution here, so just include it. If some block driver
* does not support pure options without any filename at all or
* needs some special format of the options QDict, it needs to
* implement the driver-specific bdrv_refresh_filename() function.
*/
qdict_put_obj(opts, "filename",
QOBJECT(qstring_from_str(bs->exact_filename)));
}
bs->full_open_options = opts;
}
if (bs->exact_filename[0]) {
pstrcpy(bs->filename, sizeof(bs->filename), bs->exact_filename);
} else if (bs->full_open_options) {
QString *json = qobject_to_json(QOBJECT(bs->full_open_options));
snprintf(bs->filename, sizeof(bs->filename), "json:%s",
qstring_get_str(json));
QDECREF(json);
}
}

1
include/block/block.h
View File

@ -274,6 +274,7 @@ int coroutine_fn bdrv_co_write_zeroes(BlockDriverState *bs, int64_t sector_num,
BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
const char *backing_file);
int bdrv_get_backing_file_depth(BlockDriverState *bs);
void bdrv_refresh_filename(BlockDriverState *bs);
int bdrv_truncate(BlockDriverState *bs, int64_t offset);
int64_t bdrv_nb_sectors(BlockDriverState *bs);
int64_t bdrv_getlength(BlockDriverState *bs);

6
include/block/block_int.h
View File

@ -123,6 +123,9 @@ struct BlockDriver {
int (*bdrv_create)(const char *filename, QemuOpts *opts, Error **errp);
int (*bdrv_set_key)(BlockDriverState *bs, const char *key);
int (*bdrv_make_empty)(BlockDriverState *bs);
void (*bdrv_refresh_filename)(BlockDriverState *bs);
/* aio */
BlockDriverAIOCB *(*bdrv_aio_readv)(BlockDriverState *bs,
int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
@ -323,6 +326,9 @@ struct BlockDriverState {
this file image */
char backing_format[16]; /* if non-zero and backing_file exists */
QDict *full_open_options;
char exact_filename[1024];
BlockDriverState *backing_hd;
BlockDriverState *file;