Re: [Qemu-devel] [PATCH v2 03/12] savevm: update bdrv_snapshot_find() to find snapshot by id or name and add error parameter

[Kevin Wolf <kwolf@redhat.com>]

Am 24.04.2013 um 17:32 hat Pavel Hrdina geschrieben:
> Finding snapshot by a name which could also be an id isn't best way
> how to do it. There will be rewrite of savevm, loadvm and delvm to
> improve the behavior of these commands. The savevm and loadvm will
> have their own patch series.
> 
> Now bdrv_snapshot_find takes more parameters. The name parameter will
> be matched only against the name of the snapshot and the same applies
> to id parameter.
> 
> There is one exception. If you set the last parameter, the name parameter
> will be matched against the name or the id of a snapshot. This exception
> is only for backward compatibility for other commands and it will be
> dropped after all commands will be rewritten.
> 
> We only need to know if that snapshot exists or not. We don't care
> about any error message. If snapshot exists it returns TRUE otherwise
> it returns FALSE.
> 
> There is also new Error parameter which will containt error messeage if
> something goes wrong.
> 
> Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
> ---
>  savevm.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++------------------
>  1 file changed, 67 insertions(+), 26 deletions(-)
> 
> diff --git a/savevm.c b/savevm.c
> index ba97c41..1622c55 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -2262,26 +2262,66 @@ out:
>      return ret;
>  }
>  
> -static int bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
> -                              const char *name)
> +static bool bdrv_snapshot_find(BlockDriverState *bs, QEMUSnapshotInfo *sn_info,
> +                               const char *name, const char *id, Error **errp,
> +                               bool old_match)
>  {
>      QEMUSnapshotInfo *sn_tab, *sn;
> -    int nb_sns, i, ret;
> +    int nb_sns, i;
> +    bool found = false;
> +
> +    assert(name || id);
>  
> -    ret = -ENOENT;
>      nb_sns = bdrv_snapshot_list(bs, &sn_tab);
> -    if (nb_sns < 0)
> -        return ret;
> -    for(i = 0; i < nb_sns; i++) {
> +    if (nb_sns < 0) {
> +        error_setg_errno(errp, -nb_sns, "Failed to get a snapshot list");
> +        return found;
> +    }
> +
> +    if (nb_sns == 0) {
> +        error_setg(errp, "Device has no snapshots");

This is not an error case, please remove the error_setg(). If the caller
indeed needs to have a snapshot, it can generate an error by himself. We
cannot assume here that every caller needs it.

> +        return found;
> +    }
> +
> +    for (i = 0; i < nb_sns; i++) {
>          sn = &sn_tab[i];
> -        if (!strcmp(sn->id_str, name) || !strcmp(sn->name, name)) {
> -            *sn_info = *sn;
> -            ret = 0;
> -            break;
> +        if (name && id) {
> +            if (!strcmp(sn->id_str, id) && !strcmp(sn->name, name)) {
> +                *sn_info = *sn;
> +                found = true;
> +                break;
> +            }
> +        } else if (name) {
> +            /* for compatibility for old bdrv_snapshot_find call
> +             * will be removed */
> +            if (old_match) {
> +                if (!strcmp(sn->id_str, name) || !strcmp(sn->name, name)) {
> +                    *sn_info = *sn;
> +                    found = true;
> +                    break;
> +                }
> +            } else {
> +                if (!strcmp(sn->name, name)) {
> +                    *sn_info = *sn;
> +                    found = true;
> +                    break;
> +                }
> +            }
> +        } else if (id) {
> +            if (!strcmp(sn->id_str, id)) {
> +                *sn_info = *sn;
> +                found = true;
> +                break;
> +            }
>          }
>      }
> +
> +    if (!found) {
> +        error_setg(errp, "Failed to find snapshot '%s'", name ? name : id);
> +    }

Same here.

> +
>      g_free(sn_tab);
> -    return ret;
> +    return found;
>  }
>  
>  /*
> @@ -2296,7 +2336,7 @@ static int del_existing_snapshots(Monitor *mon, const char *name)
>      bs = NULL;
>      while ((bs = bdrv_next(bs))) {
>          if (bdrv_can_snapshot(bs) &&
> -            bdrv_snapshot_find(bs, snapshot, name) >= 0)
> +            bdrv_snapshot_find(bs, snapshot, name, NULL, NULL, true))
>          {
>              bdrv_snapshot_delete(bs, name, &local_err);
>              if (error_is_set(&local_err)) {
> @@ -2358,8 +2398,7 @@ void do_savevm(Monitor *mon, const QDict *qdict)
>      sn->vm_clock_nsec = qemu_get_clock_ns(vm_clock);
>  
>      if (name) {
> -        ret = bdrv_snapshot_find(bs, old_sn, name);
> -        if (ret >= 0) {
> +        if (bdrv_snapshot_find(bs, old_sn, name, NULL, NULL, true)) {
>              pstrcpy(sn->name, sizeof(sn->name), old_sn->name);
>              pstrcpy(sn->id_str, sizeof(sn->id_str), old_sn->id_str);
>          } else {
> @@ -2440,6 +2479,7 @@ int load_vmstate(const char *name)
>      BlockDriverState *bs, *bs_vm_state;
>      QEMUSnapshotInfo sn;
>      QEMUFile *f;
> +    Error *local_err = NULL;
>      int ret;
>  
>      bs_vm_state = bdrv_snapshots();
> @@ -2449,9 +2489,10 @@ int load_vmstate(const char *name)
>      }
>  
>      /* Don't even try to load empty VM states */
> -    ret = bdrv_snapshot_find(bs_vm_state, &sn, name);
> -    if (ret < 0) {
> -        return ret;
> +    if (!bdrv_snapshot_find(bs_vm_state, &sn, name, NULL, &local_err, true)) {
> +        error_report("Snapshot doesn't exist: %s", error_get_pretty(local_err));

"Could not find snapshot" (it could just be an I/O error in reading the
snapshot list)

Or actually, this message is fine for the case where you don't find the
snapshot, but have no error in bdrv_snapshot_find().

Should the device name of bs_vm_state be mentioned in the error message?

> +        error_free(local_err);
> +        return -ENOENT;
>      } else if (sn.vm_state_size == 0) {
>          error_report("This is a disk-only snapshot. Revert to it offline "
>              "using qemu-img.");

Kevin