Re: [Qemu-devel] [PULL 02/12] sheepdog: allow to delete snapshot

[Paolo Bonzini <pbonzini@redhat.com>]

On 29/02/2016 21:08, Jeff Cody wrote:
> From: Vasiliy Tolstov <v.tolstov@selfip.ru>
> 
> This patch implements a blockdriver function bdrv_snapshot_delete() in
> the sheepdog driver. With the new function, snapshots of sheepdog can
> be deleted from libvirt.
> 
> Cc: Jeff Cody <jcody@redhat.com>
> Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
> Signed-off-by: Vasiliy Tolstov <v.tolstov@selfip.ru>
> Message-id: 1450873346-22334-1-git-send-email-mitake.hitoshi@lab.ntt.co.jp
> Signed-off-by: Jeff Cody <jcody@redhat.com>
> ---
>  block/sheepdog.c | 125 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 123 insertions(+), 2 deletions(-)
> 
> diff --git a/block/sheepdog.c b/block/sheepdog.c
> index a0098c1..8739acc 100644
> --- a/block/sheepdog.c
> +++ b/block/sheepdog.c
> @@ -284,6 +284,12 @@ static inline bool is_snapshot(struct SheepdogInode *inode)
>      return !!inode->snap_ctime;
>  }
>  
> +static inline size_t count_data_objs(const struct SheepdogInode *inode)
> +{
> +    return DIV_ROUND_UP(inode->vdi_size,
> +                        (1UL << inode->block_size_shift));
> +}
> +
>  #undef DPRINTF
>  #ifdef DEBUG_SDOG
>  #define DPRINTF(fmt, args...)                                       \
> @@ -2478,13 +2484,128 @@ out:
>      return ret;
>  }
>  
> +#define NR_BATCHED_DISCARD 128
> +
> +static bool remove_objects(BDRVSheepdogState *s)
> +{
> +    int fd, i = 0, nr_objs = 0;
> +    Error *local_err = NULL;
> +    int ret = 0;
> +    bool result = true;
> +    SheepdogInode *inode = &s->inode;
> +
> +    fd = connect_to_sdog(s, &local_err);
> +    if (fd < 0) {
> +        error_report_err(local_err);
> +        return false;
> +    }
> +
> +    nr_objs = count_data_objs(inode);
> +    while (i < nr_objs) {
> +        int start_idx, nr_filled_idx;
> +
> +        while (i < nr_objs && !inode->data_vdi_id[i]) {
> +            i++;
> +        }
> +        start_idx = i;
> +
> +        nr_filled_idx = 0;
> +        while (i < nr_objs && nr_filled_idx < NR_BATCHED_DISCARD) {
> +            if (inode->data_vdi_id[i]) {
> +                inode->data_vdi_id[i] = 0;
> +                nr_filled_idx++;
> +            }
> +
> +            i++;
> +        }
> +
> +        ret = write_object(fd, s->aio_context,
> +                           (char *)&inode->data_vdi_id[start_idx],
> +                           vid_to_vdi_oid(s->inode.vdi_id), inode->nr_copies,
> +                           (i - start_idx) * sizeof(uint32_t),
> +                           offsetof(struct SheepdogInode,
> +                                    data_vdi_id[start_idx]),
> +                           false, s->cache_flags);
> +        if (ret < 0) {
> +            error_report("failed to discard snapshot inode.");
> +            result = false;
> +            goto out;
> +        }
> +    }
> +
> +out:
> +    closesocket(fd);
> +    return result;
> +}
> +
>  static int sd_snapshot_delete(BlockDriverState *bs,
>                                const char *snapshot_id,
>                                const char *name,
>                                Error **errp)
>  {
> -    /* FIXME: Delete specified snapshot id.  */
> -    return 0;
> +    uint32_t snap_id = 0;
> +    char snap_tag[SD_MAX_VDI_TAG_LEN];
> +    Error *local_err = NULL;
> +    int fd, ret;
> +    char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN];
> +    BDRVSheepdogState *s = bs->opaque;
> +    unsigned int wlen = SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN, rlen = 0;
> +    uint32_t vid;
> +    SheepdogVdiReq hdr = {
> +        .opcode = SD_OP_DEL_VDI,
> +        .data_length = wlen,
> +        .flags = SD_FLAG_CMD_WRITE,
> +    };
> +    SheepdogVdiRsp *rsp = (SheepdogVdiRsp *)&hdr;
> +
> +    if (!remove_objects(s)) {
> +        return -1;
> +    }
> +
> +    memset(buf, 0, sizeof(buf));
> +    memset(snap_tag, 0, sizeof(snap_tag));
> +    pstrcpy(buf, SD_MAX_VDI_LEN, s->name);
> +    if (qemu_strtoul(snapshot_id, NULL, 10, (unsigned long *)&snap_id)) {

This cast seems like a very bad idea, and in fact it is.  qemu_strtoul
will access 8 bytes on 64-bit machines.  Please change snap_id to be an
unsigned long instead.

Paolo