linux-kernel - Re: [PATCH] erofs: simplify the code using for_each_set

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Message-ID: <09fdc2e3-c0ce-4c2a-8dd9-dad82e642b40@linux.alibaba.com>
Date: Wed, 17 Dec 2025 22:04:38 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Yuwen Chen <ywen.chen@...mail.com>, xiang@...nel.org
Cc: chao@...nel.org, huyue2@...lpad.com, jefflexu@...ux.alibaba.com,
 linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] erofs: simplify the code using for_each_set_bit

Hi Yuwen,

On 2025/12/17 17:09, Yuwen Chen wrote:
> When mounting the EROFS file system, it is necessary to check the
> available compression algorithms. At this time, the for_each_set_bit
> function can be used to simplify the code logic.

Anyway, I'm fine to simplify a bit.

> 
> Signed-off-by: Yuwen Chen <ywen.chen@...mail.com>
> ---
>   fs/erofs/decompressor.c | 10 +++-------
>   fs/erofs/internal.h     |  2 +-
>   2 files changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index 2ec9b2bb628d6..93e7ae2e363ff 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -405,7 +405,7 @@ int z_erofs_parse_cfgs(struct super_block *sb, struct erofs_super_block *dsb)
>   {
>   	struct erofs_sb_info *sbi = EROFS_SB(sb);
>   	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
> -	unsigned int algs, alg;
> +	unsigned int alg;

	unsigned long algs, alg;

>   	erofs_off_t offset;
>   	int size, ret = 0;
>   
> @@ -416,20 +416,16 @@ int z_erofs_parse_cfgs(struct super_block *sb, struct erofs_super_block *dsb)
>   
>   	sbi->available_compr_algs = le16_to_cpu(dsb->u1.available_compr_algs);

	algs = le16_to_cpu(dsb->u1.available_compr_algs);
	sbi->available_compr_algs = algs;
	if (algs & ~Z_EROFS_ALL_COMPR_ALGS) {
		erofs_err(sb, "unidentified algorithms %lx, please upgrade kernel",
			  algs & ~Z_EROFS_ALL_COMPR_ALGS);
		return -EOPNOTSUPP;
	}


>   	if (sbi->available_compr_algs & ~Z_EROFS_ALL_COMPR_ALGS) {
> -		erofs_err(sb, "unidentified algorithms %x, please upgrade kernel",
> +		erofs_err(sb, "unidentified algorithms %lx, please upgrade kernel",
>   			  sbi->available_compr_algs & ~Z_EROFS_ALL_COMPR_ALGS);
>   		return -EOPNOTSUPP;
>   	}
>   
>   	erofs_init_metabuf(&buf, sb);
>   	offset = EROFS_SUPER_OFFSET + sbi->sb_size;
> -	alg = 0;
> -	for (algs = sbi->available_compr_algs; algs; algs >>= 1, ++alg) {
> +	for_each_set_bit(alg, &sbi->available_compr_algs, Z_EROFS_COMPRESSION_MAX) {

	for_each_set_bit(alg, &algs, Z_EROFS_COMPRESSION_MAX) {

>   		void *data;
>   
> -		if (!(algs & 1))
> -			continue;
> -
>   		data = erofs_read_metadata(sb, &buf, &offset, &size);
>   		if (IS_ERR(data)) {
>   			ret = PTR_ERR(data);
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index c69174675caf7..c34cfcdf1e401 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -126,7 +126,7 @@ struct erofs_sb_info {
>   	struct xarray managed_pslots;
>   
>   	unsigned int shrinker_run_no;
> -	u16 available_compr_algs;
> +	unsigned long available_compr_algs;

No need to change this line.

Thanks,
Gao Xiang

>   
>   	/* pseudo inode to manage cached pages */
>   	struct inode *managed_cache;