[PATCH] nfs: add support for splice writes

[Suresh Jayaraman <sjayaraman@suse.de>]

This patch attempts to add splice writes support. In essence, it just
calls generic_file_splice_write() after doing a little sanity check.
This would allow LTTng users that are using NFS to store trace data.
There could be more applications that could be benefitted too.

I have tested this using the Jens' test program and have found no
real issues. The test program is inlined below:

/*
 * splice-out.c: Splice stdout to file
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>

#define SPLICE_SIZE (64*1024)

int main(int argc, char *argv[])
{
        int fd;

        if (argc < 2) {
                printf("%s: outfile\n", argv[0]);
                return 1;
        }

        fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644);
        if (fd < 0) {
                perror("open");
                return 1;
        }

        do {
                int ret = splice(STDIN_FILENO, NULL, fd, NULL, SPLICE_SIZE, 0);

                if (ret < 0) {
                        perror("splice");
                        break;
                } else if (ret < SPLICE_SIZE)
                        break;
        } while (1);

        close(fd);
        return 0;
}

Compile with -D _GNU_SOURCE and do something like:
	echo "some stuff" | ./splice-out <outfile>

Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
---
 fs/nfs/file.c |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 90f292b..13d6a00 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -47,6 +47,9 @@ static ssize_t nfs_file_splice_read(struct file *filp, loff_t *ppos,
 					size_t count, unsigned int flags);
 static ssize_t nfs_file_read(struct kiocb *, const struct iovec *iov,
 				unsigned long nr_segs, loff_t pos);
+static ssize_t nfs_file_splice_write(struct pipe_inode_info *pipe,
+					struct file *filp, loff_t *ppos,
+					size_t count, unsigned int flags);
 static ssize_t nfs_file_write(struct kiocb *, const struct iovec *iov,
 				unsigned long nr_segs, loff_t pos);
 static int  nfs_file_flush(struct file *, fl_owner_t id);
@@ -76,6 +79,7 @@ const struct file_operations nfs_file_operations = {
 	.lock		= nfs_lock,
 	.flock		= nfs_flock,
 	.splice_read	= nfs_file_splice_read,
+	.splice_write	= nfs_file_splice_write,
 	.check_flags	= nfs_check_flags,
 	.setlease	= nfs_setlease,
 };
@@ -550,6 +554,26 @@ out_swapfile:
 	goto out;
 }
 
+static ssize_t nfs_file_splice_write(struct pipe_inode_info *pipe,
+				     struct file *filp, loff_t *ppos,
+				     size_t count, unsigned int flags)
+{
+	struct dentry *dentry = filp->f_path.dentry;
+	struct inode *inode = dentry->d_inode;
+
+	dprintk("NFS splice_write(%s/%s, %lu@%Lu)\n",
+		dentry->d_parent->d_name.name, dentry->d_name.name,
+		(unsigned long) count, (unsigned long long) *ppos);
+
+	if (IS_SWAPFILE(inode)) {
+		printk(KERN_INFO "NFS: attempt to write to active swap"
+		       "file!\n");
+		return -EBUSY;
+	}
+
+	return generic_file_splice_write(pipe, filp, ppos, count, flags);
+}
+
 static int do_getlk(struct file *filp, int cmd, struct file_lock *fl)
 {
 	struct inode *inode = filp->f_mapping->host;