Re: [Qemu-devel] [PATCH V11 13/17] block: dump to buffer for bdrv_snapshot_dump() and bdrv_image_info_dump()

[Markus Armbruster <armbru@redhat.com>]

Wenchao Xia <xiawenc@linux.vnet.ibm.com> writes:

>   This patch would allow hmp use them just like qemu-img, and avoid
> string truncation.
>
> Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
> ---
>  block/qapi.c         |   65 +++++++++++++++++++++++++++-----------------------
>  include/block/qapi.h |    4 +-
>  qemu-img.c           |   22 ++++++++++++----
>  savevm.c             |   11 ++++++--
>  4 files changed, 61 insertions(+), 41 deletions(-)
>
> diff --git a/block/qapi.c b/block/qapi.c
> index df63c97..e27519e 100644
> --- a/block/qapi.c
> +++ b/block/qapi.c
> @@ -327,7 +327,7 @@ BlockInfoList *qmp_query_block(Error **errp)
>      return NULL;
>  }
>  
> -char *bdrv_snapshot_dump(char *buf, int buf_size, QEMUSnapshotInfo *sn)
> +void bdrv_snapshot_dump(GString *buf, QEMUSnapshotInfo *sn)
>  {
>      char buf1[128], date_buf[128], clock_buf[128];
>      struct tm tm;

I like this change, because it replaces an arbitrarily sized buffer by a
flexible one.

> @@ -335,9 +335,8 @@ char *bdrv_snapshot_dump(char *buf, int buf_size, QEMUSnapshotInfo *sn)
>      int64_t secs;
>  
>      if (!sn) {
> -        snprintf(buf, buf_size,
> -                 "%-10s%-20s%7s%20s%15s",
> -                 "ID", "TAG", "VM SIZE", "DATE", "VM CLOCK");
> +        g_string_append_printf(buf, "%-10s%-20s%7s%20s%15s",
> +                               "ID", "TAG", "VM SIZE", "DATE", "VM CLOCK");
>      } else {
>          ti = sn->date_sec;
>          localtime_r(&ti, &tm);
> @@ -350,17 +349,17 @@ char *bdrv_snapshot_dump(char *buf, int buf_size, QEMUSnapshotInfo *sn)
>                   (int)((secs / 60) % 60),
>                   (int)(secs % 60),
>                   (int)((sn->vm_clock_nsec / 1000000) % 1000));
> -        snprintf(buf, buf_size,
> -                 "%-10s%-20s%7s%20s%15s",
> -                 sn->id_str, sn->name,
> -                 get_human_readable_size(buf1, sizeof(buf1), sn->vm_state_size),
> -                 date_buf,
> -                 clock_buf);
> +        g_string_append_printf(buf,
> +                               "%-10s%-20s%7s%20s%15s",
> +                               sn->id_str, sn->name,
> +                               get_human_readable_size(buf1, sizeof(buf1),
> +                                                       sn->vm_state_size),
> +                               date_buf,
> +                               clock_buf);
>      }
> -    return buf;
>  }
>  
> -void bdrv_image_info_dump(ImageInfo *info)
> +void bdrv_image_info_dump(GString *buf, ImageInfo *info)
>  {
>      char size_buf[128], dsize_buf[128];
>      if (!info->has_actual_size) {
> @@ -370,43 +369,48 @@ void bdrv_image_info_dump(ImageInfo *info)

I don't like this change, because it introduces buffering for no
discernible reason.  Unless you can show me one, I'd like you to keep
printing directly.

>                                  info->actual_size);
>      }
>      get_human_readable_size(size_buf, sizeof(size_buf), info->virtual_size);
> -    printf("image: %s\n"
> -           "file format: %s\n"
> -           "virtual size: %s (%" PRId64 " bytes)\n"
> -           "disk size: %s\n",
> -           info->filename, info->format, size_buf,
> -           info->virtual_size,
> -           dsize_buf);
> +    g_string_append_printf(buf,
> +                           "image: %s\n"
> +                           "file format: %s\n"
> +                           "virtual size: %s (%" PRId64 " bytes)\n"
> +                           "disk size: %s\n",
> +                           info->filename, info->format, size_buf,
> +                           info->virtual_size,
> +                           dsize_buf);
>  
>      if (info->has_encrypted && info->encrypted) {
> -        printf("encrypted: yes\n");
> +        g_string_append_printf(buf, "encrypted: yes\n");
>      }
>  
>      if (info->has_cluster_size) {
> -        printf("cluster_size: %" PRId64 "\n", info->cluster_size);
> +        g_string_append_printf(buf, "cluster_size: %" PRId64 "\n",
> +                               info->cluster_size);
>      }
>  
>      if (info->has_dirty_flag && info->dirty_flag) {
> -        printf("cleanly shut down: no\n");
> +        g_string_append_printf(buf, "cleanly shut down: no\n");
>      }
>  
>      if (info->has_backing_filename) {
> -        printf("backing file: %s", info->backing_filename);
> +        g_string_append_printf(buf, "backing file: %s",
> +                               info->backing_filename);
>          if (info->has_full_backing_filename) {
> -            printf(" (actual path: %s)", info->full_backing_filename);
> +            g_string_append_printf(buf, " (actual path: %s)",
> +                                   info->full_backing_filename);
>          }
> -        putchar('\n');
> +        g_string_append_printf(buf, "\n");
>          if (info->has_backing_filename_format) {
> -            printf("backing file format: %s\n", info->backing_filename_format);
> +            g_string_append_printf(buf, "backing file format: %s\n",
> +                                   info->backing_filename_format);
>          }
>      }
>  
>      if (info->has_snapshots) {
>          SnapshotInfoList *elem;
> -        char buf[256];
>  
> -        printf("Snapshot list:\n");
> -        printf("%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
> +        g_string_append_printf(buf, "Snapshot list:\n");
> +        bdrv_snapshot_dump(buf, NULL);
> +        g_string_append_printf(buf, "\n");
>  
>          /* Ideally bdrv_snapshot_dump() would operate on SnapshotInfoList but
>           * we convert to the block layer's native QEMUSnapshotInfo for now.
> @@ -422,7 +426,8 @@ void bdrv_image_info_dump(ImageInfo *info)
>  
>              pstrcpy(sn.id_str, sizeof(sn.id_str), elem->value->id);
>              pstrcpy(sn.name, sizeof(sn.name), elem->value->name);
> -            printf("%s\n", bdrv_snapshot_dump(buf, sizeof(buf), &sn));
> +            bdrv_snapshot_dump(buf, &sn);
> +            g_string_append_printf(buf, "\n");
>          }
>      }
>  }
> diff --git a/include/block/qapi.h b/include/block/qapi.h
> index 237660f..dc1e090 100644
> --- a/include/block/qapi.h
> +++ b/include/block/qapi.h
> @@ -38,6 +38,6 @@ int bdrv_query_image_info(BlockDriverState *bs,
>  void bdrv_query_info(BlockDriverState *bs,
>                       BlockInfo **p_info,
>                       Error **errp);
> -char *bdrv_snapshot_dump(char *buf, int buf_size, QEMUSnapshotInfo *sn);
> -void bdrv_image_info_dump(ImageInfo *info);
> +void bdrv_snapshot_dump(GString *buf, QEMUSnapshotInfo *sn);
> +void bdrv_image_info_dump(GString *buf, ImageInfo *info);
>  #endif
> diff --git a/qemu-img.c b/qemu-img.c
> index 5b229a9..032f68c 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1558,18 +1558,24 @@ static void dump_snapshots(BlockDriverState *bs)
>  {
>      QEMUSnapshotInfo *sn_tab, *sn;
>      int nb_sns, i;
> -    char buf[256];
> +    GString *buf = g_string_new(NULL);
>  
>      nb_sns = bdrv_snapshot_list(bs, &sn_tab);
>      if (nb_sns <= 0)
>          return;
> -    printf("Snapshot list:\n");
> -    printf("%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
> +    g_string_append_printf(buf, "Snapshot list:\n");
> +    bdrv_snapshot_dump(buf, NULL);
> +    g_string_append_printf(buf, "\n");
>      for(i = 0; i < nb_sns; i++) {
>          sn = &sn_tab[i];
> -        printf("%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
> +        bdrv_snapshot_dump(buf, sn);
> +        g_string_append_printf(buf, "\n");
>      }
> +
> +    printf("%s", buf->str);
> +    g_string_free(buf, true);
>      g_free(sn_tab);
> +
>  }
>  
>  static void dump_json_image_info_list(ImageInfoList *list)
> @@ -1610,15 +1616,19 @@ static void dump_human_image_info_list(ImageInfoList *list)
>  {
>      ImageInfoList *elem;
>      bool delim = false;
> +    GString *buf = g_string_new(NULL);
>  
>      for (elem = list; elem; elem = elem->next) {
>          if (delim) {
> -            printf("\n");
> +            g_string_append_printf(buf, "\n");
>          }
>          delim = true;
>  
> -        bdrv_image_info_dump(elem->value);
> +        bdrv_image_info_dump(buf, elem->value);
>      }
> +
> +    printf("%s", buf->str);
> +    g_string_free(buf, true);
>  }
>  
>  static gboolean str_equal_func(gconstpointer a, gconstpointer b)
> diff --git a/savevm.c b/savevm.c
> index e4e0008..ce0bbe1 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -2466,7 +2466,7 @@ void do_info_snapshots(Monitor *mon, const QDict *qdict)
>      int nb_sns, i, ret, available;
>      int total;
>      int *available_snapshots;
> -    char buf[256];
> +    GString *buf = NULL;

Useless initialization.  But if you keep bdrv_snapshot_dump() printing,
it all goes away.

>  
>      bs = bdrv_snapshots();
>      if (!bs) {
> @@ -2509,11 +2509,16 @@ void do_info_snapshots(Monitor *mon, const QDict *qdict)
>      }
>  
>      if (total > 0) {
> -        monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), NULL));
> +        buf = g_string_new(NULL);
> +        bdrv_snapshot_dump(buf, NULL);
> +        g_string_append_printf(buf, "\n");
>          for (i = 0; i < total; i++) {
>              sn = &sn_tab[available_snapshots[i]];
> -            monitor_printf(mon, "%s\n", bdrv_snapshot_dump(buf, sizeof(buf), sn));
> +            bdrv_snapshot_dump(buf, sn);
> +            g_string_append_printf(buf, "\n");
>          }
> +        monitor_printf(mon, "%s", buf->str);
> +        g_string_free(buf, true);
>      } else {
>          monitor_printf(mon, "There is no suitable snapshot available\n");
>      }