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) 2008-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; only
  11  * version 2.1 of the License.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  *
  22  * Re-using code from kernel/relay.c, which is why it is licensed under
  23  * the GPLv2.
  24  */
  25
  26 #include <linux/module.h>
  27 #include <linux/fs.h>
  28 #include <linux/version.h>
  29
  30 #include "../../wrapper/splice.h"
  31 #include "../../wrapper/ringbuffer/backend.h"
  32 #include "../../wrapper/ringbuffer/frontend.h"
  33 #include "../../wrapper/ringbuffer/vfs.h"
  34
  35 #if 0
  36 #define printk_dbg(fmt, args...) printk(fmt, args)
  37 #else
  38 #define printk_dbg(fmt, args...)
  39 #endif
  40
  41 loff_t vfs_lib_ring_buffer_no_llseek(struct file *file, loff_t offset,
  42                 int origin)
  43 {
  44         return -ESPIPE;
  45 }
  46 EXPORT_SYMBOL_GPL(vfs_lib_ring_buffer_no_llseek);
  47
  48 /*
  49  * Release pages from the buffer so splice pipe_to_file can move them.
  50  * Called after the pipe has been populated with buffer pages.
  51  */
  52 static void lib_ring_buffer_pipe_buf_release(struct pipe_inode_info *pipe,
  53                                              struct pipe_buffer *pbuf)
  54 {
  55         __free_page(pbuf->page);
  56 }
  57
  58 static const struct pipe_buf_operations ring_buffer_pipe_buf_ops = {
  59         .can_merge = 0,
  60 #if (LINUX_VERSION_CODE < KERNEL_VERSION(3,15,0))
  61         .map = generic_pipe_buf_map,
  62         .unmap = generic_pipe_buf_unmap,
  63 #endif
  64         .confirm = generic_pipe_buf_confirm,
  65         .release = lib_ring_buffer_pipe_buf_release,
  66         .steal = generic_pipe_buf_steal,
  67         .get = generic_pipe_buf_get,
  68 };
  69
  70 /*
  71  * Page release operation after splice pipe_to_file ends.
  72  */
  73 static void lib_ring_buffer_page_release(struct splice_pipe_desc *spd,
  74                                          unsigned int i)
  75 {
  76         __free_page(spd->pages[i]);
  77 }
  78
  79 /*
  80  *      subbuf_splice_actor - splice up to one subbuf's worth of data
  81  */
  82 static int subbuf_splice_actor(struct file *in,
  83                                loff_t *ppos,
  84                                struct pipe_inode_info *pipe,
  85                                size_t len,
  86                                unsigned int flags,
  87                                struct lib_ring_buffer *buf)
  88 {
  89         struct channel *chan = buf->backend.chan;
  90         const struct lib_ring_buffer_config *config = &chan->backend.config;
  91         unsigned int poff, subbuf_pages, nr_pages;
  92         struct page *pages[PIPE_DEF_BUFFERS];
  93         struct partial_page partial[PIPE_DEF_BUFFERS];
  94         struct splice_pipe_desc spd = {
  95                 .pages = pages,
  96                 .nr_pages = 0,
  97                 .partial = partial,
  98                 .flags = flags,
  99                 .ops = &ring_buffer_pipe_buf_ops,
 100                 .spd_release = lib_ring_buffer_page_release,
 101         };
 102         unsigned long consumed_old, roffset;
 103         unsigned long bytes_avail;
 104
 105         /*
 106          * Check that a GET_SUBBUF ioctl has been done before.
 107          */
 108         WARN_ON(atomic_long_read(&buf->active_readers) != 1);
 109         consumed_old = lib_ring_buffer_get_consumed(config, buf);
 110         consumed_old += *ppos;
 111
 112         /*
 113          * Adjust read len, if longer than what is available.
 114          * Max read size is 1 subbuffer due to get_subbuf/put_subbuf for
 115          * protection.
 116          */
 117         bytes_avail = chan->backend.subbuf_size;
 118         WARN_ON(bytes_avail > chan->backend.buf_size);
 119         len = min_t(size_t, len, bytes_avail);
 120         subbuf_pages = bytes_avail >> PAGE_SHIFT;
 121         nr_pages = min_t(unsigned int, subbuf_pages, PIPE_DEF_BUFFERS);
 122         roffset = consumed_old & PAGE_MASK;
 123         poff = consumed_old & ~PAGE_MASK;
 124         printk_dbg(KERN_DEBUG "SPLICE actor len %zu pos %zd write_pos %ld\n",
 125                    len, (ssize_t)*ppos, lib_ring_buffer_get_offset(config, buf));
 126
 127         for (; spd.nr_pages < nr_pages; spd.nr_pages++) {
 128                 unsigned int this_len;
 129                 struct page **page, *new_page;
 130                 void **virt;
 131
 132                 if (!len)
 133                         break;
 134                 printk_dbg(KERN_DEBUG "SPLICE actor loop len %zu roffset %ld\n",
 135                            len, roffset);
 136
 137                 /*
 138                  * We have to replace the page we are moving into the splice
 139                  * pipe.
 140                  */
 141                 new_page = alloc_pages_node(cpu_to_node(max(buf->backend.cpu,
 142                                                             0)),
 143                                             GFP_KERNEL | __GFP_ZERO, 0);
 144                 if (!new_page)
 145                         break;
 146
 147                 this_len = PAGE_SIZE - poff;
 148                 page = lib_ring_buffer_read_get_page(&buf->backend, roffset, &virt);
 149                 spd.pages[spd.nr_pages] = *page;
 150                 *page = new_page;
 151                 *virt = page_address(new_page);
 152                 spd.partial[spd.nr_pages].offset = poff;
 153                 spd.partial[spd.nr_pages].len = this_len;
 154
 155                 poff = 0;
 156                 roffset += PAGE_SIZE;
 157                 len -= this_len;
 158         }
 159
 160         if (!spd.nr_pages)
 161                 return 0;
 162
 163         return wrapper_splice_to_pipe(pipe, &spd);
 164 }
 165
 166 ssize_t lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 167                                     struct pipe_inode_info *pipe, size_t len,
 168                                     unsigned int flags,
 169                                     struct lib_ring_buffer *buf)
 170 {
 171         struct channel *chan = buf->backend.chan;
 172         const struct lib_ring_buffer_config *config = &chan->backend.config;
 173         ssize_t spliced;
 174         int ret;
 175
 176         if (config->output != RING_BUFFER_SPLICE)
 177                 return -EINVAL;
 178
 179         /*
 180          * We require ppos and length to be page-aligned for performance reasons
 181          * (no page copy). Size is known using the ioctl
 182          * RING_BUFFER_GET_PADDED_SUBBUF_SIZE, which is page-size padded.
 183          * We fail when the ppos or len passed is not page-sized, because splice
 184          * is not allowed to copy more than the length passed as parameter (so
 185          * the ABI does not let us silently copy more than requested to include
 186          * padding).
 187          */
 188         if (*ppos != PAGE_ALIGN(*ppos) || len != PAGE_ALIGN(len))
 189                 return -EINVAL;
 190
 191         ret = 0;
 192         spliced = 0;
 193
 194         printk_dbg(KERN_DEBUG "SPLICE read len %zu pos %zd\n", len,
 195                    (ssize_t)*ppos);
 196         while (len && !spliced) {
 197                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, buf);
 198                 printk_dbg(KERN_DEBUG "SPLICE read loop ret %d\n", ret);
 199                 if (ret < 0)
 200                         break;
 201                 else if (!ret) {
 202                         if (flags & SPLICE_F_NONBLOCK)
 203                                 ret = -EAGAIN;
 204                         break;
 205                 }
 206
 207                 *ppos += ret;
 208                 if (ret > len)
 209                         len = 0;
 210                 else
 211                         len -= ret;
 212                 spliced += ret;
 213         }
 214
 215         if (spliced)
 216                 return spliced;
 217
 218         return ret;
 219 }
 220 EXPORT_SYMBOL_GPL(lib_ring_buffer_splice_read);
 221
 222 ssize_t vfs_lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 223                                     struct pipe_inode_info *pipe, size_t len,
 224                                     unsigned int flags)
 225 {
 226         struct lib_ring_buffer *buf = in->private_data;
 227
 228         return lib_ring_buffer_splice_read(in, ppos, pipe, len, flags, buf);
 229 }
 230 EXPORT_SYMBOL_GPL(vfs_lib_ring_buffer_splice_read);