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>

1 files changed, 95 insertions, 12 deletions

diff --git a/fs/pipe.c b/fs/pipe.c
index 37ba29ff3158..054b8a6a2c7a 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -11,6 +11,7 @@
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/fs.h>
+#include <linux/log2.h>
 #include <linux/mount.h>
 #include <linux/pipe_fs_i.h>
 #include <linux/uio.h>
@@ -390,7 +391,7 @@ redo:
                         if (!buf->len) {
                                 buf->ops = NULL;
                                 ops->release(pipe, buf);
-                                curbuf = (curbuf + 1) & (PIPE_BUFFERS-1);
+                                curbuf = (curbuf + 1) & (pipe->buffers - 1);
                                 pipe->curbuf = curbuf;
                                 pipe->nrbufs = --bufs;
                                 do_wakeup = 1;
@@ -472,7 +473,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
         chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
         if (pipe->nrbufs && chars != 0) {
                 int lastbuf = (pipe->curbuf + pipe->nrbufs - 1) &
-                                                        (PIPE_BUFFERS-1);
+                                                        (pipe->buffers - 1);
                 struct pipe_buffer *buf = pipe->bufs + lastbuf;
                 const struct pipe_buf_operations *ops = buf->ops;
                 int offset = buf->offset + buf->len;
@@ -518,8 +519,8 @@ redo1:
                         break;
                 }
                 bufs = pipe->nrbufs;
-                if (bufs < PIPE_BUFFERS) {
-                        int newbuf = (pipe->curbuf + bufs) & (PIPE_BUFFERS-1);
+                if (bufs < pipe->buffers) {
+                        int newbuf = (pipe->curbuf + bufs) & (pipe->buffers-1);
                         struct pipe_buffer *buf = pipe->bufs + newbuf;
                         struct page *page = pipe->tmp_page;
                         char *src;
@@ -580,7 +581,7 @@ redo2:
                         if (!total_len)
                                 break;
                 }
-                if (bufs < PIPE_BUFFERS)
+                if (bufs < pipe->buffers)
                         continue;
                 if (filp->f_flags & O_NONBLOCK) {
                         if (!ret)
@@ -640,7 +641,7 @@ static long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
                         nrbufs = pipe->nrbufs;
                         while (--nrbufs >= 0) {
                                 count += pipe->bufs[buf].len;
-                                buf = (buf+1) & (PIPE_BUFFERS-1);
+                                buf = (buf+1) & (pipe->buffers - 1);
                         }
                         mutex_unlock(&inode->i_mutex);
 
@@ -671,7 +672,7 @@ pipe_poll(struct file *filp, poll_table *wait)
         }
 
         if (filp->f_mode & FMODE_WRITE) {
-                mask |= (nrbufs < PIPE_BUFFERS) ? POLLOUT | POLLWRNORM : 0;
+                mask |= (nrbufs < pipe->buffers) ? POLLOUT | POLLWRNORM : 0;
                 /*
                  * Most Unices do not set POLLERR for FIFOs but on Linux they
                  * behave exactly like pipes for poll().
@@ -877,25 +878,32 @@ struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
 
         pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
         if (pipe) {
-                init_waitqueue_head(&pipe->wait);
-                pipe->r_counter = pipe->w_counter = 1;
-                pipe->inode = inode;
+                pipe->bufs = kzalloc(sizeof(struct pipe_buffer) * PIPE_DEF_BUFFERS, GFP_KERNEL);
+                if (pipe->bufs) {
+                        init_waitqueue_head(&pipe->wait);
+                        pipe->r_counter = pipe->w_counter = 1;
+                        pipe->inode = inode;
+                        pipe->buffers = PIPE_DEF_BUFFERS;
+                        return pipe;
+                }
+                kfree(pipe);
         }
 
-        return pipe;
+        return NULL;
 }
 
 void __free_pipe_info(struct pipe_inode_info *pipe)
 {
         int i;
 
-        for (i = 0; i < PIPE_BUFFERS; i++) {
+        for (i = 0; i < pipe->buffers; i++) {
                 struct pipe_buffer *buf = pipe->bufs + i;
                 if (buf->ops)
                         buf->ops->release(pipe, buf);
         }
         if (pipe->tmp_page)
                 __free_page(pipe->tmp_page);
+        kfree(pipe->bufs);
         kfree(pipe);
 }
 
@@ -1094,6 +1102,81 @@ SYSCALL_DEFINE1(pipe, int __user *, fildes)
 }
 
 /*
+ * Allocate a new array of pipe buffers and copy the info over. Returns the
+ * pipe size if successful, or return -ERROR on error.
+ */
+static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
+{
+        struct pipe_buffer *bufs;
+
+        /*
+         * Must be a power-of-2 currently
+         */
+        if (!is_power_of_2(arg))
+                return -EINVAL;
+
+        /*
+         * We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
+         * expect a lot of shrink+grow operations, just free and allocate
+         * again like we would do for growing. If the pipe currently
+         * contains more buffers than arg, then return busy.
+         */
+        if (arg < pipe->nrbufs)
+                return -EBUSY;
+
+        bufs = kcalloc(arg, sizeof(struct pipe_buffer), GFP_KERNEL);
+        if (unlikely(!bufs))
+                return -ENOMEM;
+
+        /*
+         * The pipe array wraps around, so just start the new one at zero
+         * and adjust the indexes.
+         */
+        if (pipe->nrbufs) {
+                const unsigned int tail = pipe->nrbufs & (pipe->buffers - 1);
+                const unsigned int head = pipe->nrbufs - tail;
+
+                if (head)
+                        memcpy(bufs, pipe->bufs + pipe->curbuf, head * sizeof(struct pipe_buffer));
+                if (tail)
+                        memcpy(bufs + head, pipe->bufs + pipe->curbuf, tail * sizeof(struct pipe_buffer));
+        }
+
+        pipe->curbuf = 0;
+        kfree(pipe->bufs);
+        pipe->bufs = bufs;
+        pipe->buffers = arg;
+        return arg;
+}
+
+long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+        struct pipe_inode_info *pipe;
+        long ret;
+
+        pipe = file->f_path.dentry->d_inode->i_pipe;
+        if (!pipe)
+                return -EBADF;
+
+        mutex_lock(&pipe->inode->i_mutex);
+
+        switch (cmd) {
+        case F_SETPIPE_SZ:
+                ret = pipe_set_size(pipe, arg);
+                break;
+        case F_GETPIPE_SZ:
+                ret = pipe->buffers;
+                break;
+        default:
+                ret = -EINVAL;
+                break;
+        }
+
+        mutex_unlock(&pipe->inode->i_mutex);
+        return ret;
+}
+
+/*
  * pipefs should _never_ be mounted by userland - too much of security hassle,
  * no real gain from having the whole whorehouse mounted. So we don't need
  * any operations on the root directory. However, we need a non-trivial