pipe: add support for shrinking and growing pipes

This patch adds F_GETPIPE_SZ and F_SETPIPE_SZ fcntl() actions for
growing and shrinking the size of a pipe and adjusts pipe.c and splice.c
(and relay and network splice) usage to work with these larger (or smaller)
pipes.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 20 insertions, 4 deletions

diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
index 86037400a6e3..afc00af3229b 100644
--- a/include/linux/fcntl.h
+++ b/include/linux/fcntl.h
@@ -22,6 +22,12 @@
 #define F_NOTIFY        (F_LINUX_SPECIFIC_BASE+2)
 
 /*
+ * Set and get of pipe page size array
+ */
+#define F_SETPIPE_SZ    (F_LINUX_SPECIFIC_BASE + 7)
+#define F_GETPIPE_SZ    (F_LINUX_SPECIFIC_BASE + 8)
+
+/*
  * Types of directory notifications that may be requested.
  */
 #define DN_ACCESS       0x00000001      /* File accessed */
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index b43a9e039059..65f4282fcbaf 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -3,7 +3,7 @@
 
 #define PIPEFS_MAGIC 0x50495045
 
-#define PIPE_BUFFERS (16)
+#define PIPE_DEF_BUFFERS        16
 
 #define PIPE_BUF_FLAG_LRU       0x01    /* page is on the LRU */
 #define PIPE_BUF_FLAG_ATOMIC    0x02    /* was atomically mapped */
@@ -44,17 +44,17 @@ struct pipe_buffer {
  **/
 struct pipe_inode_info {
         wait_queue_head_t wait;
-        unsigned int nrbufs, curbuf;
-        struct page *tmp_page;
+        unsigned int nrbufs, curbuf, buffers;
         unsigned int readers;
         unsigned int writers;
         unsigned int waiting_writers;
         unsigned int r_counter;
         unsigned int w_counter;
+        struct page *tmp_page;
         struct fasync_struct *fasync_readers;
         struct fasync_struct *fasync_writers;
         struct inode *inode;
-        struct pipe_buffer bufs[PIPE_BUFFERS];
+        struct pipe_buffer *bufs;
 };
 
 /*
@@ -154,4 +154,7 @@ int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
 int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
 void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
 
+/* for F_SETPIPE_SZ and F_GETPIPE_SZ */
+long pipe_fcntl(struct file *, unsigned int, unsigned long arg);
+
 #endif
diff --git a/include/linux/splice.h b/include/linux/splice.h
index 18e7c7c0cae6..997c3b4c212b 100644
--- a/include/linux/splice.h
+++ b/include/linux/splice.h
@@ -82,4 +82,11 @@ 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 *);
 
+/*
+ * for dynamic pipe sizing
+ */
+extern int splice_grow_spd(struct pipe_inode_info *, struct splice_pipe_desc *);
+extern void splice_shrink_spd(struct pipe_inode_info *,
+                                struct splice_pipe_desc *);
+
 #endif