Commit 83f9135b authored by Jens Axboe's avatar Jens Axboe
Browse files

[PATCH] splice: add comments documenting more of the code



Hopefully this will make Andrew a little more happy.
Signed-off-by: default avatarJens Axboe <axboe@suse.de>
parent 4f6f0bd2
......@@ -37,6 +37,12 @@ struct splice_desc {
loff_t pos; /* file position */
};
/*
* Attempt to steal a page from a pipe buffer. This should perhaps go into
* a vm helper function, it's already simplified quite a bit by the
* addition of remove_mapping(). If success is returned, the caller may
* attempt to reuse this page for another destination.
*/
static int page_cache_pipe_buf_steal(struct pipe_inode_info *info,
struct pipe_buffer *buf)
{
......@@ -108,6 +114,10 @@ static struct pipe_buf_operations page_cache_pipe_buf_ops = {
.steal = page_cache_pipe_buf_steal,
};
/*
* Pipe output worker. This sets up our pipe format with the page cache
* pipe buffer operations. Otherwise very similar to the regular pipe_writev().
*/
static ssize_t move_to_pipe(struct inode *inode, struct page **pages,
int nr_pages, unsigned long offset,
unsigned long len, unsigned int flags)
......@@ -292,6 +302,16 @@ splice_them:
return move_to_pipe(pipe, pages, i, offset, len, flags);
}
/**
* generic_file_splice_read - splice data from file to a pipe
* @in: file to splice from
* @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.
*
*/
ssize_t generic_file_splice_read(struct file *in, struct inode *pipe,
size_t len, unsigned int flags)
{
......@@ -370,10 +390,12 @@ static int pipe_to_sendpage(struct pipe_inode_info *info,
* - Destination page does not exist, we can add the pipe page to
* the page cache and avoid the copy.
*
* For now we just do the slower thing and always copy pages over, it's
* easier than migrating pages from the pipe to the target file. For the
* case of doing file | file splicing, the migrate approach had some LRU
* nastiness...
* If asked to move pages to the output file (SPLICE_F_MOVE is set in
* sd->flags), we attempt to migrate pages from the pipe to the output
* file address space page cache. This is possible if no one else has
* the pipe page referenced outside of the pipe and page cache. If
* SPLICE_F_MOVE isn't set, or we cannot move the page, we simply create
* a new page in the output file page cache and fill/dirty that.
*/
static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
struct splice_desc *sd)
......@@ -401,6 +423,10 @@ static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
* reuse buf page, if SPLICE_F_MOVE is set
*/
if (sd->flags & SPLICE_F_MOVE) {
/*
* If steal succeeds, buf->page is now pruned from the vm
* side (LRU and page cache) and we can reuse it.
*/
if (buf->ops->steal(info, buf))
goto find_page;
......@@ -484,6 +510,11 @@ out:
typedef int (splice_actor)(struct pipe_inode_info *, struct pipe_buffer *,
struct splice_desc *);
/*
* 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.
*/
static ssize_t move_from_pipe(struct inode *inode, struct file *out,
size_t len, unsigned int flags,
splice_actor *actor)
......@@ -585,6 +616,17 @@ static ssize_t move_from_pipe(struct inode *inode, struct file *out,
}
/**
* generic_file_splice_write - splice data from a pipe to a file
* @inode: pipe inode
* @out: file to write to
* @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.
*
*/
ssize_t generic_file_splice_write(struct inode *inode, struct file *out,
size_t len, unsigned int flags)
{
......@@ -611,6 +653,17 @@ ssize_t generic_file_splice_write(struct inode *inode, struct file *out,
return ret;
}
/**
* generic_splice_sendpage - splice data from a pipe to a socket
* @inode: pipe inode
* @out: socket to write to
* @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.
*
*/
ssize_t generic_splice_sendpage(struct inode *inode, struct file *out,
size_t len, unsigned int flags)
{
......@@ -620,6 +673,9 @@ ssize_t generic_splice_sendpage(struct inode *inode, struct file *out,
EXPORT_SYMBOL(generic_file_splice_write);
EXPORT_SYMBOL(generic_file_splice_read);
/*
* Attempt to initiate a splice from pipe to file.
*/
static long do_splice_from(struct inode *pipe, struct file *out, size_t len,
unsigned int flags)
{
......@@ -640,6 +696,9 @@ static long do_splice_from(struct inode *pipe, struct file *out, size_t len,
return out->f_op->splice_write(pipe, out, len, flags);
}
/*
* Attempt to initiate a splice from a file to a pipe.
*/
static long do_splice_to(struct file *in, struct inode *pipe, size_t len,
unsigned int flags)
{
......@@ -668,6 +727,9 @@ static long do_splice_to(struct file *in, struct inode *pipe, size_t len,
return in->f_op->splice_read(in, pipe, len, flags);
}
/*
* Determine where to splice to/from.
*/
static long do_splice(struct file *in, struct file *out, size_t len,
unsigned int flags)
{
......
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