Re: [PATCH] btrfs: zstd: add `zstd-fast` alias mount option for fast modes

[Qu Wenruo]

在 2025/3/31 18:53, Daniel Vacek 写道:
> Now that zstd fast compression levels are allowed with `compress=zstd:-N`
> mount option, allow also specifying the same using the `compress=zstd-fast:N`
> alias.
>
> Upstream zstd deprecated the negative levels in favor of the `zstd-fast`
> label anyways so this is actually the preferred way now. And indeed it also
> looks more human friendly.
>
> Signed-off-by: Daniel Vacek <neelx@xxxxxxxx>
> ---
>   fs/btrfs/super.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 40709e2a44fce..c1bc8d4db440a 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -368,6 +368,16 @@ static int btrfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
>   			btrfs_set_opt(ctx->mount_opt, COMPRESS);
>   			btrfs_clear_opt(ctx->mount_opt, NODATACOW);
>   			btrfs_clear_opt(ctx->mount_opt, NODATASUM);
> +		} else if (strncmp(param->string, "zstd-fast", 9) == 0) {
> +			ctx->compress_type = BTRFS_COMPRESS_ZSTD;
> +			ctx->compress_level =
> +				-btrfs_compress_str2level(BTRFS_COMPRESS_ZSTD,
> +							  param->string + 9

Can we just use some temporary variable to save the return value of 
btrfs_compress_str2level()?

);
> +			if (ctx->compress_level > 0)
> +				ctx->compress_level = -ctx->compress_level;

This also means, if we pass something like "compress=zstd-fast:-9", it 
will still set the level to the correct -9.

Not some weird double negative, which is good.

But I'm also wondering, should we even allow minus value for "zstd-fast".

> +			btrfs_set_opt(ctx->mount_opt, COMPRESS);
> +			btrfs_clear_opt(ctx->mount_opt, NODATACOW);
> +			btrfs_clear_opt(ctx->mount_opt, NODATASUM);
>   		} else if (strncmp(param->string, "zstd", 4) == 0) {
>   			ctx->compress_type = BTRFS_COMPRESS_ZSTD;
>   			ctx->compress_level =

Another thing is, if we want to prefer using zstd-fast:9 other than 
zstd:-9, should we also change our compress handling in 
btrfs_show_options() to show zstd-fast:9 instead?

Thanks,
Qu