linux-kernel - Re: [PATCH] fs: Simplify getattr interface function checking AT_GETATTR

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Message-ID: <20241101213025.GP1350452@ZenIV>
Date: Fri, 1 Nov 2024 21:30:25 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Stefan Berger <stefanb@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, Stefan Berger <stefanb@...ux.ibm.com>,
	Tyler Hicks <code@...icks.com>, ecryptfs@...r.kernel.org,
	Miklos Szeredi <miklos@...redi.hu>,
	Amir Goldstein <amir73il@...il.com>, linux-unionfs@...r.kernel.org,
	Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs: Simplify getattr interface function checking
 AT_GETATTR_NOSEC flag

On Fri, Nov 01, 2024 at 03:37:03PM -0400, Stefan Berger wrote:
> From: Stefan Berger <stefanb@...ux.ibm.com>
> 
> Commit 8a924db2d7b5 ("fs: Pass AT_GETATTR_NOSEC flag to getattr interface
> function")' introduced the AT_GETATTR_NOSEC flag to ensure that the
> call paths only call vfs_getattr_nosec if it is set instead of vfs_getattr.
> Now, simplify the getattr interface functions of filesystems where the flag
> AT_GETATTR_NOSEC is checked.
> 
> There is only a single caller of inode_operations getattr function and it
> is located in fs/stat.c in vfs_getattr_nosec. The caller there is the only
> one from which the AT_GETATTR_NOSEC flag is passed from.
> 
> Two filesystems are checking this flag in .getattr and the flag is always
> passed to them unconditionally from only vfs_getattr_nosec:
> 
> - ecryptfs:  Simplify by always calling vfs_getattr_nosec in
>              ecryptfs_getattr. From there the flag is passed to no other
>              function and this function is not called otherwise.
> 
> - overlayfs: Simplify by always calling vfs_getattr_nosec in
>              ovl_getattr. From there the flag is passed to no other
>              function and this function is not called otherwise.
> 
> The query_flags in vfs_getattr_nosec will mask-out AT_GETATTR_NOSEC from
> any caller using AT_STATX_SYNC_TYPE as mask so that the flag is not
> important inside this function. Also, since no filesystem is checking the
> flag anymore, remove the flag entirely now, including the BUG_ON check that
> never triggered.
> 
> The net change of the changes here combined with the originan commit is
> that ecryptfs and overlayfs do not call vfs_getattr but only
> vfs_getattr_nosec.
> 
> Fixes: 8a924db2d7b5 ("fs: Pass AT_GETATTR_NOSEC flag to getattr interface function")
> Reported-by: Al Viro <viro@...iv.linux.org.uk>
> Closes: https://lore.kernel.org/linux-fsdevel/20241101011724.GN1350452@ZenIV/T/#u
> Cc: Tyler Hicks <code@...icks.com>
> Cc: ecryptfs@...r.kernel.org
> Cc: Miklos Szeredi <miklos@...redi.hu>
> Cc: Amir Goldstein <amir73il@...il.com>
> Cc: linux-unionfs@...r.kernel.org
> Cc: Christian Brauner <brauner@...nel.org>
> Cc: linux-fsdevel@...r.kernel.org
> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>

Applied (viro/vfs.git#work.statx2)