[PATCH 1/5] vmsplice: open-code do_writev and do_readv

[Askar Safin <safinaskar@gmail.com>]

My previous vmsplice patch did the following mistake: I did
"CLASS(fd, f)(fd)", then did some checks on resulting "struct file",
then passed numeric (!) file descriptor to a function.

This is somewhat okay in this particular case, but I still think
this is code smell, so I fix this by open-coding do_writev and do_readv.

Also I insert a comment to warn other developers to keep
do_writev and do_readv in sync with vmsplice(2).

Signed-off-by: Askar Safin <safinaskar@gmail.com>
---
 fs/read_write.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 1e5444f4d..e224e7cb8 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1070,6 +1070,7 @@ static ssize_t vfs_writev(struct file *file, const struct iovec __user *vec,
 static ssize_t do_readv(unsigned long fd, const struct iovec __user *vec,
 			unsigned long vlen, rwf_t flags)
 {
+	/* All future changes to this function should be kept in sync with vmsplice(2). */
 	CLASS(fd_pos, f)(fd);
 	ssize_t ret = -EBADF;
 
@@ -1093,6 +1094,7 @@ static ssize_t do_readv(unsigned long fd, const struct iovec __user *vec,
 static ssize_t do_writev(unsigned long fd, const struct iovec __user *vec,
 			 unsigned long vlen, rwf_t flags)
 {
+	/* All future changes to this function should be kept in sync with vmsplice(2). */
 	CLASS(fd_pos, f)(fd);
 	ssize_t ret = -EBADF;
 
@@ -1226,14 +1228,24 @@ SYSCALL_DEFINE4(vmsplice, unsigned long, fd, const struct iovec __user *, vec,
 	if (fd_empty(f))
 		return -EBADF;
 
-	/* We do do_writev/do_readv, so it is okay to pass "false" here */
+	/* We do vfs_writev/vfs_readv, so it is okay to pass "false" here */
 	if (!get_pipe_info(fd_file(f), /* for_splice = */ false))
 		return -EBADF;
 
-	if (fd_file(f)->f_mode & FMODE_WRITE)
-		return do_writev(fd, vec, vlen, (flags & SPLICE_F_NONBLOCK) ? RWF_NOWAIT : 0);
-	else
-		return do_readv(fd, vec, vlen, (flags & SPLICE_F_NONBLOCK) ? RWF_NOWAIT : 0);
+	if (fd_file(f)->f_mode & FMODE_WRITE) {
+		ssize_t ret = vfs_writev(fd_file(f), vec, vlen, NULL, (flags & SPLICE_F_NONBLOCK) ? RWF_NOWAIT : 0);
+		if (ret > 0)
+			add_wchar(current, ret);
+		inc_syscw(current);
+		return ret;
+	} else {
+		ssize_t ret = vfs_readv(fd_file(f), vec, vlen, NULL, (flags & SPLICE_F_NONBLOCK) ? RWF_NOWAIT : 0);
+
+		if (ret > 0)
+			add_rchar(current, ret);
+		inc_syscr(current);
+		return ret;
+	}
 }
 
 /*
-- 
2.47.3