Re: [PATCH v21 03/30] splice: Rename direct_splice_read() to copy_splice_read()

David Howells
2023-05-22T07:55:26Z

> For the future it'd be nice if exported functions would always get
> proper kernel doc,

Something like the attached?

David
---
commit 0362042ba0751fc5457b0548fb9006f9d7dfbeca
Author: David Howells <dhowells@redhat.com>
Date: Mon May 22 08:34:24 2023 +0100

splice: kdoc for filemap_splice_read() and copy_splice_read()

Provide kerneldoc comments for filemap_splice_read() and
copy_splice_read().

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Christoph Hellwig <hch@lst.de>
cc: Jens Axboe <axboe@kernel.dk>
cc: Steve French <smfrench@gmail.com>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: linux-mm@kvack.org
cc: linux-block@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org

diff --git a/fs/splice.c b/fs/splice.c
index 9be4cb3b9879..5292a8fa929d 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -299,8 +299,25 @@ void splice_shrink_spd(struct splice_pipe_desc *spd)
kfree(spd->partial);
}

-/*
- * Copy data from a file into pages and then splice those into the output pipe.
+/**
+ * copy_splice_read - Copy data from a file and splice the copy into a pipe
+ * @in: The file to read from
+ * @ppos: Pointer to the file position to read from
+ * @pipe: The pipe to splice into
+ * @len: The amount to splice
+ * @flags: The SPLICE_F_* flags
+ *
+ * This function allocates a bunch of pages sufficient to hold the requested
+ * amount of data (but limited by the remaining pipe capacity), passes it to
+ * the file's ->read_iter() to read into and then splices the used pages into
+ * the pipe.
+ *
+ * On success, the number of bytes read will be returned and *@ppos will be
+ * updated if appropriate; 0 will be returned if there is no more data to be
+ * read; -EAGAIN will be returned if the pipe had no space, and some other
+ * negative error code will be returned on error. A short read may occur if
+ * the pipe has insufficient space, we reach the end of the data or we hit a
+ * hole.
*/
ssize_t copy_splice_read(struct file *in, loff_t *ppos,
struct pipe_inode_info *pipe,
diff --git a/mm/filemap.c b/mm/filemap.c
index 603b562d69b1..1f235a6430fd 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2871,9 +2871,24 @@ size_t splice_folio_into_pipe(struct pipe_inode_info *pipe,
return spliced;
}

-/*
- * Splice folios from the pagecache of a buffered (ie. non-O_DIRECT) file into
- * a pipe.
+/**
+ * filemap_splice_read - Splice data from a file's pagecache into a pipe
+ * @in: The file to read from
+ * @ppos: Pointer to the file position to read from
+ * @pipe: The pipe to splice into
+ * @len: The amount to splice
+ * @flags: The SPLICE_F_* flags
+ *
+ * This function gets folios from a file's pagecache and splices them into the
+ * pipe. Readahead will be called as necessary to fill more folios. This may
+ * be used for blockdevs also.
+ *
+ * On success, the number of bytes read will be returned and *@ppos will be
+ * updated if appropriate; 0 will be returned if there is no more data to be
+ * read; -EAGAIN will be returned if the pipe had no space, and some other
+ * negative error code will be returned on error. A short read may occur if
+ * the pipe has insufficient space, we reach the end of the data or we hit a
+ * hole.
*/
ssize_t filemap_splice_read(struct file *in, loff_t *ppos,
struct pipe_inode_info *pipe,