Re: [PATCH 07/14] block/blklogwrites: drop error propagation

[Greg Kurz <groug@kaod.org>]

On Wed,  9 Sep 2020 21:59:23 +0300
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:

> It's simple to avoid error propagation in blk_log_writes_open(), we
> just need to refactor blk_log_writes_find_cur_log_sector() a bit.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/blklogwrites.c | 23 +++++++++++------------
>  1 file changed, 11 insertions(+), 12 deletions(-)
> 
> diff --git a/block/blklogwrites.c b/block/blklogwrites.c
> index 7ef046cee9..c7da507b2d 100644
> --- a/block/blklogwrites.c
> +++ b/block/blklogwrites.c
> @@ -96,10 +96,10 @@ static inline bool blk_log_writes_sector_size_valid(uint32_t sector_size)
>          sector_size < (1ull << 24);
>  }
>  
> -static uint64_t blk_log_writes_find_cur_log_sector(BdrvChild *log,
> -                                                   uint32_t sector_size,
> -                                                   uint64_t nr_entries,
> -                                                   Error **errp)
> +static int64_t blk_log_writes_find_cur_log_sector(BdrvChild *log,
> +                                                  uint32_t sector_size,
> +                                                  uint64_t nr_entries,
> +                                                  Error **errp)
>  {
>      uint64_t cur_sector = 1;
>      uint64_t cur_idx = 0;
> @@ -112,13 +112,13 @@ static uint64_t blk_log_writes_find_cur_log_sector(BdrvChild *log,
>          if (read_ret < 0) {
>              error_setg_errno(errp, -read_ret,
>                               "Failed to read log entry %"PRIu64, cur_idx);
> -            return (uint64_t)-1ull;
> +            return read_ret;

This changes the error status of blk_log_writes_open() from -EINVAL to
whatever is returned by bdrv_pread(). I guess this is an improvement
worth to be mentioned in the changelog.

>          }
>  
>          if (cur_entry.flags & ~cpu_to_le64(LOG_FLAG_MASK)) {
>              error_setg(errp, "Invalid flags 0x%"PRIx64" in log entry %"PRIu64,
>                         le64_to_cpu(cur_entry.flags), cur_idx);
> -            return (uint64_t)-1ull;
> +            return -EINVAL;
>          }
>  
>          /* Account for the sector of the entry itself */
> @@ -143,7 +143,6 @@ static int blk_log_writes_open(BlockDriverState *bs, QDict *options, int flags,
>  {
>      BDRVBlkLogWritesState *s = bs->opaque;
>      QemuOpts *opts;
> -    Error *local_err = NULL;
>      int ret;
>      uint64_t log_sector_size;
>      bool log_append;
> @@ -215,15 +214,15 @@ static int blk_log_writes_open(BlockDriverState *bs, QDict *options, int flags,
>          s->nr_entries = 0;
>  
>          if (blk_log_writes_sector_size_valid(log_sector_size)) {
> -            s->cur_log_sector =
> +            int64_t cur_log_sector =
>                  blk_log_writes_find_cur_log_sector(s->log_file, log_sector_size,
> -                                    le64_to_cpu(log_sb.nr_entries), &local_err);
> -            if (local_err) {
> -                ret = -EINVAL;
> -                error_propagate(errp, local_err);
> +                                    le64_to_cpu(log_sb.nr_entries), errp);
> +            if (cur_log_sector < 0) {
> +                ret = cur_log_sector;

This is converting int64_t to int, which is usually not recommended.
In practice this is probably okay because cur_log_sector is supposed
to be a negative errno (ie. an int) in this case.

Maybe make this clear with a an assert(cur_log_sector >= INT_MIN) ?

>                  goto fail_log;
>              }
>  
> +            s->cur_log_sector = cur_log_sector;
>              s->nr_entries = le64_to_cpu(log_sb.nr_entries);
>          }
>      } else {