lib/ringbuffer/ring_buffer_splice.c

   1 /*
   2  * ring_buffer_splice.c
   3  *
   4  * Copyright (C) 2002-2005 - Tom Zanussi <zanussi@us.ibm.com>, IBM Corp
   5  * Copyright (C) 1999-2005 - Karim Yaghmour <karim@opersys.com>
   6  * Copyright (C) 2008-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * Re-using content from kernel/relay.c.
   9  *
  10  * This file is released under the GPL v2.
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/fs.h>
  15
  16 #include "../../wrapper/splice.h"
  17 #include "../../wrapper/ringbuffer/backend.h"
  18 #include "../../wrapper/ringbuffer/frontend.h"
  19 #include "../../wrapper/ringbuffer/vfs.h"
  20
  21 #if 0
  22 #define printk_dbg(fmt, args...) printk(fmt, args)
  23 #else
  24 #define printk_dbg(fmt, args...)
  25 #endif
  26
  27 loff_t lib_ring_buffer_no_llseek(struct file *file, loff_t offset, int origin)
  28 {
  29         return -ESPIPE;
  30 }
  31
  32 /*
  33  * Release pages from the buffer so splice pipe_to_file can move them.
  34  * Called after the pipe has been populated with buffer pages.
  35  */
  36 static void lib_ring_buffer_pipe_buf_release(struct pipe_inode_info *pipe,
  37                                              struct pipe_buffer *pbuf)
  38 {
  39         __free_page(pbuf->page);
  40 }
  41
  42 static const struct pipe_buf_operations ring_buffer_pipe_buf_ops = {
  43         .can_merge = 0,
  44         .map = generic_pipe_buf_map,
  45         .unmap = generic_pipe_buf_unmap,
  46         .confirm = generic_pipe_buf_confirm,
  47         .release = lib_ring_buffer_pipe_buf_release,
  48         .steal = generic_pipe_buf_steal,
  49         .get = generic_pipe_buf_get,
  50 };
  51
  52 /*
  53  * Page release operation after splice pipe_to_file ends.
  54  */
  55 static void lib_ring_buffer_page_release(struct splice_pipe_desc *spd,
  56                                          unsigned int i)
  57 {
  58         __free_page(spd->pages[i]);
  59 }
  60
  61 /*
  62  *      subbuf_splice_actor - splice up to one subbuf's worth of data
  63  */
  64 static int subbuf_splice_actor(struct file *in,
  65                                loff_t *ppos,
  66                                struct pipe_inode_info *pipe,
  67                                size_t len,
  68                                unsigned int flags)
  69 {
  70         struct lib_ring_buffer *buf = in->private_data;
  71         struct channel *chan = buf->backend.chan;
  72         const struct lib_ring_buffer_config *config = &chan->backend.config;
  73         unsigned int poff, subbuf_pages, nr_pages;
  74         struct page *pages[PIPE_DEF_BUFFERS];
  75         struct partial_page partial[PIPE_DEF_BUFFERS];
  76         struct splice_pipe_desc spd = {
  77                 .pages = pages,
  78                 .nr_pages = 0,
  79                 .partial = partial,
  80                 .flags = flags,
  81                 .ops = &ring_buffer_pipe_buf_ops,
  82                 .spd_release = lib_ring_buffer_page_release,
  83         };
  84         unsigned long consumed_old, roffset;
  85         unsigned long bytes_avail;
  86
  87         /*
  88          * Check that a GET_SUBBUF ioctl has been done before.
  89          */
  90         WARN_ON(atomic_long_read(&buf->active_readers) != 1);
  91         consumed_old = lib_ring_buffer_get_consumed(config, buf);
  92         consumed_old += *ppos;
  93
  94         /*
  95          * Adjust read len, if longer than what is available.
  96          * Max read size is 1 subbuffer due to get_subbuf/put_subbuf for
  97          * protection.
  98          */
  99         bytes_avail = chan->backend.subbuf_size;
 100         WARN_ON(bytes_avail > chan->backend.buf_size);
 101         len = min_t(size_t, len, bytes_avail);
 102         subbuf_pages = bytes_avail >> PAGE_SHIFT;
 103         nr_pages = min_t(unsigned int, subbuf_pages, PIPE_DEF_BUFFERS);
 104         roffset = consumed_old & PAGE_MASK;
 105         poff = consumed_old & ~PAGE_MASK;
 106         printk_dbg(KERN_DEBUG "SPLICE actor len %zu pos %zd write_pos %ld\n",
 107                    len, (ssize_t)*ppos, lib_ring_buffer_get_offset(config, buf));
 108
 109         for (; spd.nr_pages < nr_pages; spd.nr_pages++) {
 110                 unsigned int this_len;
 111                 struct page **page, *new_page;
 112                 void **virt;
 113
 114                 if (!len)
 115                         break;
 116                 printk_dbg(KERN_DEBUG "SPLICE actor loop len %zu roffset %ld\n",
 117                            len, roffset);
 118
 119                 /*
 120                  * We have to replace the page we are moving into the splice
 121                  * pipe.
 122                  */
 123                 new_page = alloc_pages_node(cpu_to_node(max(buf->backend.cpu,
 124                                                             0)),
 125                                             GFP_KERNEL | __GFP_ZERO, 0);
 126                 if (!new_page)
 127                         break;
 128
 129                 this_len = PAGE_SIZE - poff;
 130                 page = lib_ring_buffer_read_get_page(&buf->backend, roffset, &virt);
 131                 spd.pages[spd.nr_pages] = *page;
 132                 *page = new_page;
 133                 *virt = page_address(new_page);
 134                 spd.partial[spd.nr_pages].offset = poff;
 135                 spd.partial[spd.nr_pages].len = this_len;
 136
 137                 poff = 0;
 138                 roffset += PAGE_SIZE;
 139                 len -= this_len;
 140         }
 141
 142         if (!spd.nr_pages)
 143                 return 0;
 144
 145         return wrapper_splice_to_pipe(pipe, &spd);
 146 }
 147
 148 ssize_t lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 149                                     struct pipe_inode_info *pipe, size_t len,
 150                                     unsigned int flags)
 151 {
 152         struct lib_ring_buffer *buf = in->private_data;
 153         struct channel *chan = buf->backend.chan;
 154         const struct lib_ring_buffer_config *config = &chan->backend.config;
 155         ssize_t spliced;
 156         int ret;
 157
 158         if (config->output != RING_BUFFER_SPLICE)
 159                 return -EINVAL;
 160
 161         /*
 162          * We require ppos and length to be page-aligned for performance reasons
 163          * (no page copy). Size is known using the ioctl
 164          * RING_BUFFER_GET_PADDED_SUBBUF_SIZE, which is page-size padded.
 165          * We fail when the ppos or len passed is not page-sized, because splice
 166          * is not allowed to copy more than the length passed as parameter (so
 167          * the ABI does not let us silently copy more than requested to include
 168          * padding).
 169          */
 170         if (*ppos != PAGE_ALIGN(*ppos) || len != PAGE_ALIGN(len))
 171                 return -EINVAL;
 172
 173         ret = 0;
 174         spliced = 0;
 175
 176         printk_dbg(KERN_DEBUG "SPLICE read len %zu pos %zd\n", len,
 177                    (ssize_t)*ppos);
 178         while (len && !spliced) {
 179                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags);
 180                 printk_dbg(KERN_DEBUG "SPLICE read loop ret %d\n", ret);
 181                 if (ret < 0)
 182                         break;
 183                 else if (!ret) {
 184                         if (flags & SPLICE_F_NONBLOCK)
 185                                 ret = -EAGAIN;
 186                         break;
 187                 }
 188
 189                 *ppos += ret;
 190                 if (ret > len)
 191                         len = 0;
 192                 else
 193                         len -= ret;
 194                 spliced += ret;
 195         }
 196
 197         if (spliced)
 198                 return spliced;
 199
 200         return ret;
 201 }
 202 EXPORT_SYMBOL_GPL(lib_ring_buffer_splice_read);