cachefiles: Fix the incorrect return value in __cachefiles_write()

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.

 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@huawei.com>
Link: https://lore.kernel.org/20250703024418.2809353-1-wozizhi@huaweicloud.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index c08e4a66ac07a76e36bbc6a098e4b555807ae9b9..3e0576d9db1d2f64a972bf672d5e3ac2fc680884 100644 (file)
--- 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 d9bc6717612829e5777b441c51749d2d1ef107c1..a7ed86fa98bb8c5a635cb4821cfee8536cb427db 100644 (file)
--- 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);