On Apr 17, 2018, at 1:19 PM, Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote:
>
> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
>
> In unix_zeroout() for files, we should try a ZERO_RANGE before we try
> PUNCH_HOLE because the former will not cause us to lose preallocated
> blocks. Since block devices have supported fallocate for a few years
> now, refactor the fallocate calls into a helper and call it from either
> case.
>
> Reported-by: Andreas Dilger <adilger@xxxxxxxxx>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
The patch was a bit confusing to read (I thought it skipped zero-out
for block devices), but looking at the whole code it is clear that the
__unix_zeroout() is always being called, and the truncate() code block
is only being called for regular files.
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> ---
> lib/ext2fs/unix_io.c | 53 ++++++++++++++++++++++++++++----------------------
> 1 file changed, 30 insertions(+), 23 deletions(-)
>
>
> diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
> index c6b058d..1fb6279 100644
> --- a/lib/ext2fs/unix_io.c
> +++ b/lib/ext2fs/unix_io.c
> @@ -1118,6 +1118,31 @@ static errcode_t unix_discard(io_channel channel, unsigned long long block,
> return EXT2_ET_UNIMPLEMENTED;
> }
>
> +/*
> + * If we know about ZERO_RANGE, try that before we try PUNCH_HOLE because
> + * ZERO_RANGE doesn't unmap preallocated blocks. We prefer fallocate because
> + * it always invalidates page cache, and libext2fs requires that reads after
> + * ZERO_RANGE return zeroes.
> + */
> +static int __unix_zeroout(int fd, off_t offset, off_t len)
> +{
> + int ret = -1;
> +
> +#if defined(HAVE_FALLOCATE) && defined(FALLOC_FL_ZERO_RANGE)
> + ret = fallocate(fd, FALLOC_FL_ZERO_RANGE, offset, len);
> + if (ret == 0)
> + return 0;
> +#endif
> +#if defined(HAVE_FALLOCATE) && defined(FALLOC_FL_PUNCH_HOLE) && defined(FALLOC_FL_KEEP_SIZE)
> + ret = fallocate(fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> + offset, len);
> + if (ret == 0)
> + return 0;
> +#endif
> + errno = EOPNOTSUPP;
> + return ret;
> +}
> +
> /* parameters might not be used if OS doesn't support zeroout */
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wunused-parameter"
> @@ -1134,10 +1159,7 @@ static errcode_t unix_zeroout(io_channel channel, unsigned long long block,
> if (safe_getenv("UNIX_IO_NOZEROOUT"))
> goto unimplemented;
>
> - if (channel->flags & CHANNEL_FLAGS_BLOCK_DEVICE) {
> - /* Not implemented until the BLKZEROOUT mess is fixed */
> - goto unimplemented;
> - } else {
> + if (!(channel->flags & CHANNEL_FLAGS_BLOCK_DEVICE)) {
> /* Regular file, try to use truncate/punch/zero. */
> struct stat statbuf;
>
> @@ -1157,26 +1179,11 @@ static errcode_t unix_zeroout(io_channel channel, unsigned long long block,
> if (ret)
> goto err;
> }
> -#if defined(HAVE_FALLOCATE) && (defined(FALLOC_FL_ZERO_RANGE) || \
> - (defined(FALLOC_FL_PUNCH_HOLE) && defined(FALLOC_FL_KEEP_SIZE)))
> -#if defined(FALLOC_FL_PUNCH_HOLE) && defined(FALLOC_FL_KEEP_SIZE)
> - ret = fallocate(data->dev,
> - FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> - (off_t)(block) * channel->block_size + data->offset,
> - (off_t)(count) * channel->block_size);
> - if (ret == 0)
> - goto err;
> -#endif
> -#ifdef FALLOC_FL_ZERO_RANGE
> - ret = fallocate(data->dev,
> - FALLOC_FL_ZERO_RANGE,
> - (off_t)(block) * channel->block_size + data->offset,
> - (off_t)(count) * channel->block_size);
> -#endif
> -#else
> - goto unimplemented;
> -#endif /* HAVE_FALLOCATE && (ZERO_RANGE || (PUNCH_HOLE && KEEP_SIZE)) */
> }
> +
> + ret = __unix_zeroout(data->dev,
> + (off_t)(block) * channel->block_size + data->offset,
> + (off_t)(count) * channel->block_size);
> err:
> if (ret < 0) {
> if (errno == EOPNOTSUPP)
>
Cheers, Andreas
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