drivers/staging/lttng/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
  29 #include "../../wrapper/splice.h"
  30 #include "../../wrapper/ringbuffer/backend.h"
  31 #include "../../wrapper/ringbuffer/frontend.h"
  32 #include "../../wrapper/ringbuffer/vfs.h"
  33
  34 #if 0
  35 #define printk_dbg(fmt, args...) printk(fmt, args)
  36 #else
  37 #define printk_dbg(fmt, args...)
  38 #endif
  39
  40 loff_t vfs_lib_ring_buffer_no_llseek(struct file *file, loff_t offset,
  41                 int origin)
  42 {
  43         return -ESPIPE;
  44 }
  45 EXPORT_SYMBOL_GPL(vfs_lib_ring_buffer_no_llseek);
  46
  47 /*
  48  * Release pages from the buffer so splice pipe_to_file can move them.
  49  * Called after the pipe has been populated with buffer pages.
  50  */
  51 static void lib_ring_buffer_pipe_buf_release(struct pipe_inode_info *pipe,
  52                                              struct pipe_buffer *pbuf)
  53 {
  54         __free_page(pbuf->page);
  55 }
  56
  57 static const struct pipe_buf_operations ring_buffer_pipe_buf_ops = {
  58         .can_merge = 0,
  59         .map = generic_pipe_buf_map,
  60         .unmap = generic_pipe_buf_unmap,
  61         .confirm = generic_pipe_buf_confirm,
  62         .release = lib_ring_buffer_pipe_buf_release,
  63         .steal = generic_pipe_buf_steal,
  64         .get = generic_pipe_buf_get,
  65 };
  66
  67 /*
  68  * Page release operation after splice pipe_to_file ends.
  69  */
  70 static void lib_ring_buffer_page_release(struct splice_pipe_desc *spd,
  71                                          unsigned int i)
  72 {
  73         __free_page(spd->pages[i]);
  74 }
  75
  76 /*
  77  *      subbuf_splice_actor - splice up to one subbuf's worth of data
  78  */
  79 static int subbuf_splice_actor(struct file *in,
  80                                loff_t *ppos,
  81                                struct pipe_inode_info *pipe,
  82                                size_t len,
  83                                unsigned int flags,
  84                                struct lib_ring_buffer *buf)
  85 {
  86         struct channel *chan = buf->backend.chan;
  87         const struct lib_ring_buffer_config *config = &chan->backend.config;
  88         unsigned int poff, subbuf_pages, nr_pages;
  89         struct page *pages[PIPE_DEF_BUFFERS];
  90         struct partial_page partial[PIPE_DEF_BUFFERS];
  91         struct splice_pipe_desc spd = {
  92                 .pages = pages,
  93                 .nr_pages = 0,
  94                 .partial = partial,
  95                 .flags = flags,
  96                 .ops = &ring_buffer_pipe_buf_ops,
  97                 .spd_release = lib_ring_buffer_page_release,
  98         };
  99         unsigned long consumed_old, roffset;
 100         unsigned long bytes_avail;
 101
 102         /*
 103          * Check that a GET_SUBBUF ioctl has been done before.
 104          */
 105         WARN_ON(atomic_long_read(&buf->active_readers) != 1);
 106         consumed_old = lib_ring_buffer_get_consumed(config, buf);
 107         consumed_old += *ppos;
 108
 109         /*
 110          * Adjust read len, if longer than what is available.
 111          * Max read size is 1 subbuffer due to get_subbuf/put_subbuf for
 112          * protection.
 113          */
 114         bytes_avail = chan->backend.subbuf_size;
 115         WARN_ON(bytes_avail > chan->backend.buf_size);
 116         len = min_t(size_t, len, bytes_avail);
 117         subbuf_pages = bytes_avail >> PAGE_SHIFT;
 118         nr_pages = min_t(unsigned int, subbuf_pages, PIPE_DEF_BUFFERS);
 119         roffset = consumed_old & PAGE_MASK;
 120         poff = consumed_old & ~PAGE_MASK;
 121         printk_dbg(KERN_DEBUG "SPLICE actor len %zu pos %zd write_pos %ld\n",
 122                    len, (ssize_t)*ppos, lib_ring_buffer_get_offset(config, buf));
 123
 124         for (; spd.nr_pages < nr_pages; spd.nr_pages++) {
 125                 unsigned int this_len;
 126                 struct page **page, *new_page;
 127                 void **virt;
 128
 129                 if (!len)
 130                         break;
 131                 printk_dbg(KERN_DEBUG "SPLICE actor loop len %zu roffset %ld\n",
 132                            len, roffset);
 133
 134                 /*
 135                  * We have to replace the page we are moving into the splice
 136                  * pipe.
 137                  */
 138                 new_page = alloc_pages_node(cpu_to_node(max(buf->backend.cpu,
 139                                                             0)),
 140                                             GFP_KERNEL | __GFP_ZERO, 0);
 141                 if (!new_page)
 142                         break;
 143
 144                 this_len = PAGE_SIZE - poff;
 145                 page = lib_ring_buffer_read_get_page(&buf->backend, roffset, &virt);
 146                 spd.pages[spd.nr_pages] = *page;
 147                 *page = new_page;
 148                 *virt = page_address(new_page);
 149                 spd.partial[spd.nr_pages].offset = poff;
 150                 spd.partial[spd.nr_pages].len = this_len;
 151
 152                 poff = 0;
 153                 roffset += PAGE_SIZE;
 154                 len -= this_len;
 155         }
 156
 157         if (!spd.nr_pages)
 158                 return 0;
 159
 160         return wrapper_splice_to_pipe(pipe, &spd);
 161 }
 162
 163 ssize_t lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 164                                     struct pipe_inode_info *pipe, size_t len,
 165                                     unsigned int flags,
 166                                     struct lib_ring_buffer *buf)
 167 {
 168         struct channel *chan = buf->backend.chan;
 169         const struct lib_ring_buffer_config *config = &chan->backend.config;
 170         ssize_t spliced;
 171         int ret;
 172
 173         if (config->output != RING_BUFFER_SPLICE)
 174                 return -EINVAL;
 175
 176         /*
 177          * We require ppos and length to be page-aligned for performance reasons
 178          * (no page copy). Size is known using the ioctl
 179          * RING_BUFFER_GET_PADDED_SUBBUF_SIZE, which is page-size padded.
 180          * We fail when the ppos or len passed is not page-sized, because splice
 181          * is not allowed to copy more than the length passed as parameter (so
 182          * the ABI does not let us silently copy more than requested to include
 183          * padding).
 184          */
 185         if (*ppos != PAGE_ALIGN(*ppos) || len != PAGE_ALIGN(len))
 186                 return -EINVAL;
 187
 188         ret = 0;
 189         spliced = 0;
 190
 191         printk_dbg(KERN_DEBUG "SPLICE read len %zu pos %zd\n", len,
 192                    (ssize_t)*ppos);
 193         while (len && !spliced) {
 194                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, buf);
 195                 printk_dbg(KERN_DEBUG "SPLICE read loop ret %d\n", ret);
 196                 if (ret < 0)
 197                         break;
 198                 else if (!ret) {
 199                         if (flags & SPLICE_F_NONBLOCK)
 200                                 ret = -EAGAIN;
 201                         break;
 202                 }
 203
 204                 *ppos += ret;
 205                 if (ret > len)
 206                         len = 0;
 207                 else
 208                         len -= ret;
 209                 spliced += ret;
 210         }
 211
 212         if (spliced)
 213                 return spliced;
 214
 215         return ret;
 216 }
 217 EXPORT_SYMBOL_GPL(lib_ring_buffer_splice_read);
 218
 219 ssize_t vfs_lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 220                                     struct pipe_inode_info *pipe, size_t len,
 221                                     unsigned int flags)
 222 {
 223         struct lib_ring_buffer *buf = in->private_data;
 224
 225         return lib_ring_buffer_splice_read(in, ppos, pipe, len, flags, buf);
 226 }
 227 EXPORT_SYMBOL_GPL(vfs_lib_ring_buffer_splice_read);