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Subject[PATCH 16/18] splice: completely document external interface with kerneldoc
Date
Also add fs/splice.c as a kerneldoc target with a smaller blurb that
should be expanded to better explain the overview of splice.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
Documentation/DocBook/kernel-api.tmpl | 11 ++++
fs/splice.c | 101 +++++++++++++++++++++++++++------
2 files changed, 94 insertions(+), 18 deletions(-)

diff --git a/Documentation/DocBook/kernel-api.tmpl b/Documentation/DocBook/kernel-api.tmpl
index 38f88b6..8c5698a 100644
--- a/Documentation/DocBook/kernel-api.tmpl
+++ b/Documentation/DocBook/kernel-api.tmpl
@@ -643,4 +643,15 @@ X!Idrivers/video/console/fonts.c
!Edrivers/spi/spi.c
</chapter>

+ <chapter id="splice">
+ <title>splice API</title>
+ <para>)
+ splice is a method for moving blocks of data around inside the
+ kernel, without continually transferring it between the kernel
+ and user space.
+ </para>
+!Iinclude/linux/splice.h
+!Ffs/splice.c
+ </chapter>
+
</book>
diff --git a/fs/splice.c b/fs/splice.c
index ff62ac9..f24e367 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -153,9 +153,16 @@ static const struct pipe_buf_operations user_page_pipe_buf_ops = {
.get = generic_pipe_buf_get,
};

-/*
- * Pipe output worker. This fills a pipe with the information contained
- * from splice_pipe_desc().
+/**
+ * splice_to_pipe - fill passed data into a pipe
+ * @pipe: pipe to fill
+ * @spd: data to fill
+ *
+ * Description:
+ * @spd contains a map of pages and len/offset tupples, a long with
+ * the struct pipe_buf_operations associated with these pages. This
+ * function will link that data to the pipe.
+ *
*/
ssize_t splice_to_pipe(struct pipe_inode_info *pipe,
struct splice_pipe_desc *spd)
@@ -453,11 +460,16 @@ fill_it:
/**
* generic_file_splice_read - splice data from file to a pipe
* @in: file to splice from
+ * @ppos: position in @in
* @pipe: pipe to splice to
* @len: number of bytes to splice
* @flags: splice modifier flags
*
- * Will read pages from given file and fill them into a pipe.
+ * Description:
+ * Will read pages from given file and fill them into a pipe. Can be
+ * used as long as the address_space operations for the source implements
+ * a readpage() hook.
+ *
*/
ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
struct pipe_inode_info *pipe, size_t len,
@@ -646,10 +658,18 @@ out_ret:
return ret;
}

-/*
- * Pipe input worker. Most of this logic works like a regular pipe, the
- * key here is the 'actor' worker passed in that actually moves the data
- * to the wanted destination. See pipe_to_file/pipe_to_sendpage above.
+/**
+ * __splice_from_pipe - splice data from a pipe to given actor
+ * @pipe: pipe to splice from
+ * @sd: information to @actor
+ * @actor: handler that splices the data
+ *
+ * Description:
+ * This function does little more than loop over the pipe and call
+ * @actor to do the actual moving of a single struct pipe_buffer to
+ * the desired destination. See pipe_to_file, pipe_to_sendpage, or
+ * pipe_to_user.
+ *
*/
ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
splice_actor *actor)
@@ -742,6 +762,20 @@ ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
}
EXPORT_SYMBOL(__splice_from_pipe);

+/**
+ * splice_from_pipe - splice data from a pipe to a file
+ * @pipe: pipe to splice from
+ * @out: file to splice to
+ * @ppos: position in @out
+ * @len: how many bytes to splice
+ * @flags: splice modifier flags
+ * @actor: handler that splices the data
+ *
+ * Description:
+ * See __splice_from_pipe. This function locks the input and output inodes,
+ * otherwise it's identical to __splice_from_pipe().
+ *
+ */
ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
loff_t *ppos, size_t len, unsigned int flags,
splice_actor *actor)
@@ -773,12 +807,14 @@ ssize_t splice_from_pipe(struct pipe_inode_info *pipe, struct file *out,
* generic_file_splice_write_nolock - generic_file_splice_write without mutexes
* @pipe: pipe info
* @out: file to write to
+ * @ppos: position in @out
* @len: number of bytes to splice
* @flags: splice modifier flags
*
- * Will either move or copy pages (determined by @flags options) from
- * the given pipe inode to the given file. The caller is responsible
- * for acquiring i_mutex on both inodes.
+ * Description:
+ * Will either move or copy pages (determined by @flags options) from
+ * the given pipe inode to the given file. The caller is responsible
+ * for acquiring i_mutex on both inodes.
*
*/
ssize_t
@@ -827,11 +863,13 @@ EXPORT_SYMBOL(generic_file_splice_write_nolock);
* generic_file_splice_write - splice data from a pipe to a file
* @pipe: pipe info
* @out: file to write to
+ * @ppos: position in @out
* @len: number of bytes to splice
* @flags: splice modifier flags
*
- * Will either move or copy pages (determined by @flags options) from
- * the given pipe inode to the given file.
+ * Description:
+ * Will either move or copy pages (determined by @flags options) from
+ * the given pipe inode to the given file.
*
*/
ssize_t
@@ -879,13 +917,15 @@ EXPORT_SYMBOL(generic_file_splice_write);

/**
* generic_splice_sendpage - splice data from a pipe to a socket
- * @inode: pipe inode
+ * @pipe: pipe to splice from
* @out: socket to write to
+ * @ppos: position in @out
* @len: number of bytes to splice
* @flags: splice modifier flags
*
- * Will send @len bytes from the pipe to a network socket. No data copying
- * is involved.
+ * Description:
+ * Will send @len bytes from the pipe to a network socket. No data copying
+ * is involved.
*
*/
ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
@@ -939,8 +979,18 @@ static long do_splice_to(struct file *in, loff_t *ppos,
return in->f_op->splice_read(in, ppos, pipe, len, flags);
}

-/*
- * Splices from an input file to an actor, using a 'direct' pipe.
+/**
+ * splice_direct_to_actor - splices data directly between two non-pipes
+ * @in: file to splice from
+ * @sd: actor information on where to splice to
+ * @actor: handles the data splicing
+ *
+ * Description:
+ * This is a special case helper to splice directly between two
+ * points, without requiring an explicit pipe. Internally an allocated
+ * pipe is cached in the process, and reused during the life time of
+ * that process.
+ *
*/
ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
splice_direct_actor *actor)
@@ -1070,6 +1120,21 @@ static int direct_splice_actor(struct pipe_inode_info *pipe,
return do_splice_from(pipe, file, &sd->pos, sd->total_len, sd->flags);
}

+/**
+ * do_splice_direct - splices data directly between two files
+ * @in: file to splice from
+ * @ppos: input file offset
+ * @out: file to splice to
+ * @len: number of bytes to splice
+ * @flags: splice modifier flags
+ *
+ * Description:
+ * For use by do_sendfile(). splice can easily emulate sendfile, but
+ * doing it in the application would incur an extra system call
+ * (splice in + splice out, as compared to just sendfile()). So this helper
+ * can splice directly through a process-private pipe.
+ *
+ */
long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
size_t len, unsigned int flags)
{
--
1.5.2.1.174.gcd03
-
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