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Subject[RFC v17][PATCH 43/60] splice: export pipe/file-to-pipe/file functionality
Date
During pipes c/r pipes we need to save and restore pipe buffers. But
do_splice() requires two file descriptors, therefore we can't use it,
as we always have one file descriptor (checkpoint image) and one
pipe_inode_info.

This patch exports interfaces that work at the pipe_inode_info level,
namely link_pipe(), do_splice_to() and do_splice_from(). They are used
in the following patch to to save and restore pipe buffers without
unnecessary data copy.

It slightly modifies both do_splice_to() and do_splice_from() to
detect the case of pipe-to-pipe transfer, in which case they invoke
splice_pipe_to_pipe() directly.

Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
---
fs/splice.c | 61 ++++++++++++++++++++++++++++++++---------------
include/linux/splice.h | 9 +++++++
2 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 73766d2..f251b4c 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1055,18 +1055,43 @@ ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
EXPORT_SYMBOL(generic_splice_sendpage);

/*
+ * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
+ * location, so checking ->i_pipe is not enough to verify that this is a
+ * pipe.
+ */
+static inline struct pipe_inode_info *pipe_info(struct inode *inode)
+{
+ if (S_ISFIFO(inode->i_mode))
+ return inode->i_pipe;
+
+ return NULL;
+}
+
+static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
+ struct pipe_inode_info *opipe,
+ size_t len, unsigned int flags);
+
+/*
* Attempt to initiate a splice from pipe to file.
*/
-static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
- loff_t *ppos, size_t len, unsigned int flags)
+long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
+ loff_t *ppos, size_t len, unsigned int flags)
{
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *,
loff_t *, size_t, unsigned int);
+ struct pipe_inode_info *opipe;
int ret;

if (unlikely(!(out->f_mode & FMODE_WRITE)))
return -EBADF;

+ /* When called directly (e.g. from c/r) output may be a pipe */
+ opipe = pipe_info(out->f_path.dentry->d_inode);
+ if (opipe) {
+ BUG_ON(opipe == pipe);
+ return splice_pipe_to_pipe(pipe, opipe, len, flags);
+ }
+
if (unlikely(out->f_flags & O_APPEND))
return -EINVAL;

@@ -1084,17 +1109,25 @@ static long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
/*
* Attempt to initiate a splice from a file to a pipe.
*/
-static long do_splice_to(struct file *in, loff_t *ppos,
- struct pipe_inode_info *pipe, size_t len,
- unsigned int flags)
+long do_splice_to(struct file *in, loff_t *ppos,
+ struct pipe_inode_info *pipe, size_t len,
+ unsigned int flags)
{
ssize_t (*splice_read)(struct file *, loff_t *,
struct pipe_inode_info *, size_t, unsigned int);
+ struct pipe_inode_info *ipipe;
int ret;

if (unlikely(!(in->f_mode & FMODE_READ)))
return -EBADF;

+ /* When called firectly (e.g. from c/r) input may be a pipe */
+ ipipe = pipe_info(in->f_path.dentry->d_inode);
+ if (ipipe) {
+ BUG_ON(ipipe == pipe);
+ return splice_pipe_to_pipe(ipipe, pipe, len, flags);
+ }
+
ret = rw_verify_area(READ, in, ppos, len);
if (unlikely(ret < 0))
return ret;
@@ -1273,18 +1306,6 @@ long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
struct pipe_inode_info *opipe,
size_t len, unsigned int flags);
-/*
- * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
- * location, so checking ->i_pipe is not enough to verify that this is a
- * pipe.
- */
-static inline struct pipe_inode_info *pipe_info(struct inode *inode)
-{
- if (S_ISFIFO(inode->i_mode))
- return inode->i_pipe;
-
- return NULL;
-}

/*
* Determine where to splice to/from.
@@ -1887,9 +1908,9 @@ retry:
/*
* Link contents of ipipe to opipe.
*/
-static int link_pipe(struct pipe_inode_info *ipipe,
- struct pipe_inode_info *opipe,
- size_t len, unsigned int flags)
+int link_pipe(struct pipe_inode_info *ipipe,
+ struct pipe_inode_info *opipe,
+ size_t len, unsigned int flags)
{
struct pipe_buffer *ibuf, *obuf;
int ret = 0, i = 0, nbuf;
diff --git a/include/linux/splice.h b/include/linux/splice.h
index 18e7c7c..431662c 100644
--- a/include/linux/splice.h
+++ b/include/linux/splice.h
@@ -82,4 +82,13 @@ extern ssize_t splice_to_pipe(struct pipe_inode_info *,
extern ssize_t splice_direct_to_actor(struct file *, struct splice_desc *,
splice_direct_actor *);

+extern int link_pipe(struct pipe_inode_info *ipipe,
+ struct pipe_inode_info *opipe,
+ size_t len, unsigned int flags);
+extern long do_splice_to(struct file *in, loff_t *ppos,
+ struct pipe_inode_info *pipe, size_t len,
+ unsigned int flags);
+extern long do_splice_from(struct pipe_inode_info *pipe, struct file *out,
+ loff_t *ppos, size_t len, unsigned int flags);
+
#endif
--
1.6.0.4


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