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

Tejun Heo
2009-05-21T07:29:30Z

Eric W. Biederman wrote:
> From: Eric W. Biederman <ebiederm@xmission.com>
>
> 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@aristanetworks.com>
> ---
> 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