linux-kernel - [PATCH] fs: 9p: add generic splice

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Date:   Tue,  1 Dec 2020 14:54:09 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Eric Van Hensbergen <ericvh@...il.com>,
        Latchesar Ionkov <lucho@...kov.net>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>
Subject: [PATCH] fs: 9p: add generic splice_read file operations

The v9fs file operations were missing the splice_read operations, which
breaks sendfile() of files on such a filesystem. I discovered this while
trying to load an eBPF program using iproute2 inside a 'virtme' environment
which uses 9pfs for the virtual file system. iproute2 relies on sendfile()
with an AF_ALG socket to hash files, which was erroring out in the virtual
environment.

Since generic_file_splice_read() seems to just implement splice_read in
terms of the read_iter operation, I simply added the generic implementation
to the file operations, which fixed the error I was seeing. A quick grep
indicates that this is what most other file systems do as well.

The only caveat is that my test case was only hitting the
v9fs_file_operations_dotl implementation. I added it to the other file
operations structs as well because it seemed like the sensible thing to do
given that they all implement read_iter, but those are only compile tested.

Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
 fs/9p/vfs_file.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index b177fd3b1eb3..01026b47018c 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -655,6 +655,7 @@ const struct file_operations v9fs_cached_file_operations = {
 	.release = v9fs_dir_release,
 	.lock = v9fs_file_lock,
 	.mmap = v9fs_file_mmap,
+	.splice_read = generic_file_splice_read,
 	.fsync = v9fs_file_fsync,
 };
 
@@ -667,6 +668,7 @@ const struct file_operations v9fs_cached_file_operations_dotl = {
 	.lock = v9fs_file_lock_dotl,
 	.flock = v9fs_file_flock_dotl,
 	.mmap = v9fs_file_mmap,
+	.splice_read = generic_file_splice_read,
 	.fsync = v9fs_file_fsync_dotl,
 };
 
@@ -678,6 +680,7 @@ const struct file_operations v9fs_file_operations = {
 	.release = v9fs_dir_release,
 	.lock = v9fs_file_lock,
 	.mmap = generic_file_readonly_mmap,
+	.splice_read = generic_file_splice_read,
 	.fsync = v9fs_file_fsync,
 };
 
@@ -690,6 +693,7 @@ const struct file_operations v9fs_file_operations_dotl = {
 	.lock = v9fs_file_lock_dotl,
 	.flock = v9fs_file_flock_dotl,
 	.mmap = generic_file_readonly_mmap,
+	.splice_read = generic_file_splice_read,
 	.fsync = v9fs_file_fsync_dotl,
 };
 
@@ -701,6 +705,7 @@ const struct file_operations v9fs_mmap_file_operations = {
 	.release = v9fs_dir_release,
 	.lock = v9fs_file_lock,
 	.mmap = v9fs_mmap_file_mmap,
+	.splice_read = generic_file_splice_read,
 	.fsync = v9fs_file_fsync,
 };
 
@@ -713,5 +718,6 @@ const struct file_operations v9fs_mmap_file_operations_dotl = {
 	.lock = v9fs_file_lock_dotl,
 	.flock = v9fs_file_flock_dotl,
 	.mmap = v9fs_mmap_file_mmap,
+	.splice_read = generic_file_splice_read,
 	.fsync = v9fs_file_fsync_dotl,
 };
-- 
2.29.2