linux-kernel - Re: [PATCH] cachefiles: Fix the incorrect return value in __cachefiles

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Message-ID: <66b2f540-228f-40e9-9ac5-529e3101e973@huaweicloud.com>
Date: Thu, 3 Jul 2025 11:02:46 +0800
From: Zizhi Wo <wozizhi@...weicloud.com>
To: Zizhi Wo <wozizhi@...weicloud.com>, netfs@...ts.linux.dev,
 dhowells@...hat.com, jlayton@...nel.org, brauner@...nel.org
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 libaokun1@...wei.com, yangerkun@...wei.com, houtao1@...wei.com,
 yukuai3@...wei.com
Subject: Re: [PATCH] cachefiles: Fix the incorrect return value in
 __cachefiles_write()



在 2025/7/3 10:44, Zizhi Wo 写道:
> From: Zizhi Wo <wozizhi@...wei.com>
> 
> In __cachefiles_write(), if the return value of the write operation > 0, it
> is set to 0. This makes it impossible to distinguish scenarios where a
> partial write has occurred, and will affect the outer calling functions:
> 
>   1) cachefiles_write_complete() will call "term_func" such as
> netfs_write_subrequest_terminated(). When "ret" in __cachefiles_write()
> is used as the "transferred_or_error" of this function, it can not
> distinguish the amount of data written, makes the WARN meaningless.
> 

Sorry, I was negligent. The first error actually doesn't exist because
ret=0 was set after cachefiles_write_complete(), but the second error
still exists.

Thanks,
Zizhi Wo

>   2) cachefiles_ondemand_fd_write_iter() can only assume all writes were
> successful by default when "ret" is 0, and unconditionally return the full
> length specified by user space.
> 
> Fix it by modifying "ret" to reflect the actual number of bytes written.
> Furthermore, returning a value greater than 0 from __cachefiles_write()
> does not affect other call paths, such as cachefiles_issue_write() and
> fscache_write().
> 
> Fixes: 047487c947e8 ("cachefiles: Implement the I/O routines")
> Signed-off-by: Zizhi Wo <wozizhi@...wei.com>
> ---
>   fs/cachefiles/io.c       | 2 --
>   fs/cachefiles/ondemand.c | 4 +---
>   2 files changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
> index c08e4a66ac07..3e0576d9db1d 100644
> --- a/fs/cachefiles/io.c
> +++ b/fs/cachefiles/io.c
> @@ -347,8 +347,6 @@ int __cachefiles_write(struct cachefiles_object *object,
>   	default:
>   		ki->was_async = false;
>   		cachefiles_write_complete(&ki->iocb, ret);
> -		if (ret > 0)
> -			ret = 0;
>   		break;
>   	}
>   
> diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
> index d9bc67176128..a7ed86fa98bb 100644
> --- a/fs/cachefiles/ondemand.c
> +++ b/fs/cachefiles/ondemand.c
> @@ -83,10 +83,8 @@ static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb,
>   
>   	trace_cachefiles_ondemand_fd_write(object, file_inode(file), pos, len);
>   	ret = __cachefiles_write(object, file, pos, iter, NULL, NULL);
> -	if (!ret) {
> -		ret = len;
> +	if (ret > 0)
>   		kiocb->ki_pos += ret;
> -	}
>   
>   out:
>   	fput(file);