Re: [Qemu-devel] [PATCH V5 2/5] qemu-nbd: support internal snapshot export

[Kevin Wolf]

Am 10.11.2013 um 23:03 hat Wenchao Xia geschrieben:
> Now it is possible to directly export an internal snapshot, which
> can be used to probe the snapshot's contents without qemu-img
> convert.
> 
> Signed-off-by: Wenchao Xia <address@hidden>
> ---
>  block/snapshot.c         |   18 +++++++++++++++++
>  include/block/snapshot.h |    8 +++++++
>  qemu-nbd.c               |   47 ++++++++++++++++++++++++++++++++++++++++++++-
>  qemu-nbd.texi            |    8 ++++++-
>  4 files changed, 78 insertions(+), 3 deletions(-)
> 
> diff --git a/block/snapshot.c b/block/snapshot.c
> index e51a7db..7cc45fa 100644
> --- a/block/snapshot.c
> +++ b/block/snapshot.c
> @@ -25,6 +25,24 @@
>  #include "block/snapshot.h"
>  #include "block/block_int.h"
>  
> +QemuOptsList internal_snapshot_opts = {
> +    .name = "snapshot",
> +    .head = QTAILQ_HEAD_INITIALIZER(internal_snapshot_opts.head),
> +    .desc = {
> +        {
> +            .name = SNAPSHOT_OPT_ID,
> +            .type = QEMU_OPT_STRING,
> +            .help = "snapshot id"
> +        },{
> +            .name = SNAPSHOT_OPT_NAME,
> +            .type = QEMU_OPT_STRING,
> +            .help = "snapshot name"
> +        },{
> +            /* end of list */
> +        }
> +    },
> +};
> +
>  int bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
>                         const char *name)
>  {
> diff --git a/include/block/snapshot.h b/include/block/snapshot.h
> index d05bea7..770d9bb 100644
> --- a/include/block/snapshot.h
> +++ b/include/block/snapshot.h
> @@ -27,6 +27,14 @@
>  
>  #include "qemu-common.h"
>  #include "qapi/error.h"
> +#include "qemu/option.h"
> +
> +
> +#define SNAPSHOT_OPT_BASE       "snapshot."
> +#define SNAPSHOT_OPT_ID         "snapshot.id"
> +#define SNAPSHOT_OPT_NAME       "snapshot.name"
> +
> +extern QemuOptsList internal_snapshot_opts;
>  
>  typedef struct QEMUSnapshotInfo {
>      char id_str[128]; /* unique snapshot id */
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index c26c98e..f934eaa 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -20,6 +20,7 @@
>  #include "block/block.h"
>  #include "block/nbd.h"
>  #include "qemu/main-loop.h"
> +#include "block/snapshot.h"
>  
>  #include <stdarg.h>
>  #include <stdio.h>
> @@ -79,7 +80,14 @@ static void usage(const char *name)
>  "\n"
>  "Block device options:\n"
>  "  -r, --read-only      export read-only\n"
> -"  -s, --snapshot       use snapshot file\n"
> +"  -s, --snapshot       use FILE as an external snapshot, create a 
> temporary\n"
> +"                       file with backing_file=FILE, redirect the write to\n"
> +"                       the temporary one\n"
> +"  -l, --load-snapshot=SNAPSHOT_PARAM\n"
> +"                       load an internal snapshot inside FILE and export 
> it\n"
> +"                       as an read-only device, SNAPSHOT_PARAM format is\n"
> +"                       'snapshot.id=[ID],snapshot.name=[NAME]', or\n"
> +"                       '[ID_OR_NAME]'\n"
>  "  -n, --nocache        disable host cache\n"
>  "      --cache=MODE     set cache mode (none, writeback, ...)\n"
>  #ifdef CONFIG_LINUX_AIO
> @@ -315,7 +323,9 @@ int main(int argc, char **argv)
>      char *device = NULL;
>      int port = NBD_DEFAULT_PORT;
>      off_t fd_size;
> -    const char *sopt = "hVb:o:p:rsnP:c:dvk:e:f:t";
> +    QemuOpts *sn_opts = NULL;
> +    const char *sn_id_or_name = NULL;
> +    const char *sopt = "hVb:o:p:rsnP:c:dvk:e:f:tl:";
>      struct option lopt[] = {
>          { "help", 0, NULL, 'h' },
>          { "version", 0, NULL, 'V' },
> @@ -328,6 +338,7 @@ int main(int argc, char **argv)
>          { "connect", 1, NULL, 'c' },
>          { "disconnect", 0, NULL, 'd' },
>          { "snapshot", 0, NULL, 's' },
> +        { "load-snapshot", 1, NULL, 'l' },
>          { "nocache", 0, NULL, 'n' },
>          { "cache", 1, NULL, QEMU_NBD_OPT_CACHE },
>  #ifdef CONFIG_LINUX_AIO
> @@ -428,6 +439,18 @@ int main(int argc, char **argv)
>                  errx(EXIT_FAILURE, "Offset must be positive `%s'", optarg);
>              }
>              break;
> +        case 'l':
> +            if (strncmp(optarg, SNAPSHOT_OPT_BASE, strlen(SNAPSHOT_OPT_BASE))
> +                == 0) {

You can avoid this ugly line break by using strstart():

    if (strstart(optarg, SNAPSHOT_OPT_BASE, NULL)) {
        ...

Kevin