Re: [PATCH 08/20] sysfs: Optimize just changing the sysfs file mode.

[Tejun Heo]

Eric W. Biederman wrote:
> From: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> 
> Don't allocate a struct iattr for the sysfs dentry if just
> the mode changes because we have a field for that on the
> sysfs_dirent, and we can trigger that case with sysfs_chmod_file.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxxxxxxxx>
> ---
>  fs/sysfs/inode.c |   22 ++++++++++++++--------
>  1 files changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
> index 555f0ff..70ff2a2 100644
> --- a/fs/sysfs/inode.c
> +++ b/fs/sysfs/inode.c
> @@ -60,12 +60,16 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
>  		return error;
>  
>  	iattr->ia_valid &= ~ATTR_SIZE; /* ignore size changes */
> +	if (iattr->ia_valid & ATTR_MODE) {
> +		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
> +			iattr->ia_mode &= ~S_ISGID;
> +	}
>  
>  	error = inode_setattr(inode, iattr);
>  	if (error)
>  		return error;
>  
> -	if (!sd_iattr) {
> +	if (!sd_iattr && (ia_valid & ~ATTR_MODE)) {
>  		/* setting attributes for the first time, allocate now */
>  		sd_iattr = kzalloc(sizeof(struct iattr), GFP_KERNEL);
>  		if (!sd_iattr)
> @@ -78,6 +82,13 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
>  		sd->s_iattr = sd_iattr;
>  	}
>  
> +	if (ia_valid & ATTR_MODE)
> +		sd->s_mode = iattr->ia_mode;
> +
> +	/* If we don't need the extra attributes leave */
> +	if (!sd_iattr)
> +		return 0;

One visible difference is lack of timestamp update.  Is there any use
case where sysfs file mode changing needs to be fast?

Thanks.

-- 
tejun
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