linux-kernel - Re: [PATCH RESEND V12 1/8] fs: Generic function to convert iocb to rw flags

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Date:   Wed, 24 Mar 2021 15:43:12 +0800
From:   Rokudo Yan <wu-yan@....com>
To:     Alessio Balsini <balsini@...roid.com>,
        Miklos Szeredi <miklos@...redi.hu>
CC:     Akilesh Kailash <akailash@...gle.com>,
        Amir Goldstein <amir73il@...il.com>,
        Antonio SJ Musumeci <trapexit@...wn.link>,
        "David Anderson" <dvander@...gle.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        "Jann Horn" <jannh@...gle.com>, Jens Axboe <axboe@...nel.dk>,
        Martijn Coenen <maco@...roid.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Lawrence <paullawrence@...gle.com>,
        Peng Tao <bergwolf@...il.com>,
        Stefano Duo <duostefano93@...il.com>,
        Zimuzo Ezeozue <zezeozue@...gle.com>,
        <fuse-devel@...ts.sourceforge.net>, <kernel-team@...roid.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND V12 1/8] fs: Generic function to convert iocb to rw
 flags

On 1/26/21 12:46 AM, Alessio Balsini wrote:
> On Mon, Jan 25, 2021 at 03:30:50PM +0000, Alessio Balsini wrote:
>> OverlayFS implements its own function to translate iocb flags into rw
>> flags, so that they can be passed into another vfs call.
>> With commit ce71bfea207b4 ("fs: align IOCB_* flags with RWF_* flags")
>> Jens created a 1:1 matching between the iocb flags and rw flags,
>> simplifying the conversion.
>>
>> Reduce the OverlayFS code by making the flag conversion function generic
>> and reusable.
>>
>> Signed-off-by: Alessio Balsini <balsini@...roid.com>
>> ---
>>   fs/overlayfs/file.c | 23 +++++------------------
>>   include/linux/fs.h  |  5 +++++
>>   2 files changed, 10 insertions(+), 18 deletions(-)
>>
>> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
>> index bd9dd38347ae..56be2ffc5a14 100644
>> --- a/fs/overlayfs/file.c
>> +++ b/fs/overlayfs/file.c
>> @@ -15,6 +15,8 @@
>>   #include <linux/fs.h>
>>   #include "overlayfs.h"
>>   
>> +#define OVL_IOCB_MASK (IOCB_DSYNC | IOCB_HIPRI | IOCB_NOWAIT | IOCB_SYNC)
>> +
>>   struct ovl_aio_req {
>>   	struct kiocb iocb;
>>   	struct kiocb *orig_iocb;
>> @@ -236,22 +238,6 @@ static void ovl_file_accessed(struct file *file)
>>   	touch_atime(&file->f_path);
>>   }
>>   
>> -static rwf_t ovl_iocb_to_rwf(int ifl)
>> -{
>> -	rwf_t flags = 0;
>> -
>> -	if (ifl & IOCB_NOWAIT)
>> -		flags |= RWF_NOWAIT;
>> -	if (ifl & IOCB_HIPRI)
>> -		flags |= RWF_HIPRI;
>> -	if (ifl & IOCB_DSYNC)
>> -		flags |= RWF_DSYNC;
>> -	if (ifl & IOCB_SYNC)
>> -		flags |= RWF_SYNC;
>> -
>> -	return flags;
>> -}
>> -
>>   static void ovl_aio_cleanup_handler(struct ovl_aio_req *aio_req)
>>   {
>>   	struct kiocb *iocb = &aio_req->iocb;
>> @@ -299,7 +285,8 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
>>   	old_cred = ovl_override_creds(file_inode(file)->i_sb);
>>   	if (is_sync_kiocb(iocb)) {
>>   		ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,
>> -				    ovl_iocb_to_rwf(iocb->ki_flags));
>> +				    iocb_to_rw_flags(iocb->ki_flags,
>> +						     OVL_IOCB_MASK));
>>   	} else {
>>   		struct ovl_aio_req *aio_req;
>>   
>> @@ -356,7 +343,7 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
>>   	if (is_sync_kiocb(iocb)) {
>>   		file_start_write(real.file);
>>   		ret = vfs_iter_write(real.file, iter, &iocb->ki_pos,
>> -				     ovl_iocb_to_rwf(ifl));
>> +				     iocb_to_rw_flags(ifl, OVL_IOCB_MASK));
>>   		file_end_write(real.file);
>>   		/* Update size */
>>   		ovl_copyattr(ovl_inode_real(inode), inode);
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index fd47deea7c17..647c35423545 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -3275,6 +3275,11 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>>   	return 0;
>>   }
>>   
>> +static inline rwf_t iocb_to_rw_flags(int ifl, int iocb_mask)
>> +{
>> +	return ifl & iocb_mask;
>> +}
>> +
>>   static inline ino_t parent_ino(struct dentry *dentry)
>>   {
>>   	ino_t res;
>> -- 
>> 2.30.0.280.ga3ce27912f-goog
>>
> 
> For some reason lkml.org and lore.kernel.org are not showing this change
> as part of the thread.
> Let's see if replying to the email fixes the indexing.
> 
> Regards,
> Alessio
> 

Hi, Alessio

This change imply IOCB_* and RWF_* flags are properly aligned, which is 
not true for kernel version 5.4/4.19/4.14. As the patch ("fs: align 
IOCB_* flags with RWF_* flags") is not back-ported to these stable 
kernel branches. The issue was found when applying these patches
to kernel-5.4(files open with passthrough enabled can't do append 
write). I think the issue exists in AOSP common kernel too.
Could you please fix this?

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ce71bfea207b4d7c21d36f24ec37618ffcea1da8

https://android-review.googlesource.com/c/kernel/common/+/1556243

Thanks
yanwu