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 #if (LINUX_VERSION_CODE < KERNEL_VERSION(4,12,0))
  99                 .flags = flags,
 100 #endif
 101                 .ops = &ring_buffer_pipe_buf_ops,
 102                 .spd_release = lib_ring_buffer_page_release,
 103         };
 104         unsigned long consumed_old, roffset;
 105         unsigned long bytes_avail;
 106
 107         /*
 108          * Check that a GET_SUBBUF ioctl has been done before.
 109          */
 110         WARN_ON(atomic_long_read(&buf->active_readers) != 1);
 111         consumed_old = lib_ring_buffer_get_consumed(config, buf);
 112         consumed_old += *ppos;
 113
 114         /*
 115          * Adjust read len, if longer than what is available.
 116          * Max read size is 1 subbuffer due to get_subbuf/put_subbuf for
 117          * protection.
 118          */
 119         bytes_avail = chan->backend.subbuf_size;
 120         WARN_ON(bytes_avail > chan->backend.buf_size);
 121         len = min_t(size_t, len, bytes_avail);
 122         subbuf_pages = bytes_avail >> PAGE_SHIFT;
 123         nr_pages = min_t(unsigned int, subbuf_pages, PIPE_DEF_BUFFERS);
 124         roffset = consumed_old & PAGE_MASK;
 125         poff = consumed_old & ~PAGE_MASK;
 126         printk_dbg(KERN_DEBUG "SPLICE actor len %zu pos %zd write_pos %ld\n",
 127                    len, (ssize_t)*ppos, lib_ring_buffer_get_offset(config, buf));
 128
 129         for (; spd.nr_pages < nr_pages; spd.nr_pages++) {
 130                 unsigned int this_len;
 131                 unsigned long *pfnp, new_pfn;
 132                 struct page *new_page;
 133                 void **virt;
 134
 135                 if (!len)
 136                         break;
 137                 printk_dbg(KERN_DEBUG "SPLICE actor loop len %zu roffset %ld\n",
 138                            len, roffset);
 139
 140                 /*
 141                  * We have to replace the page we are moving into the splice
 142                  * pipe.
 143                  */
 144                 new_page = alloc_pages_node(cpu_to_node(max(buf->backend.cpu,
 145                                                             0)),
 146                                             GFP_KERNEL | __GFP_ZERO, 0);
 147                 if (!new_page)
 148                         break;
 149                 new_pfn = page_to_pfn(new_page);
 150                 this_len = PAGE_SIZE - poff;
 151                 pfnp = lib_ring_buffer_read_get_pfn(&buf->backend, roffset, &virt);
 152                 spd.pages[spd.nr_pages] = pfn_to_page(*pfnp);
 153                 *pfnp = new_pfn;
 154                 *virt = page_address(new_page);
 155                 spd.partial[spd.nr_pages].offset = poff;
 156                 spd.partial[spd.nr_pages].len = this_len;
 157
 158                 poff = 0;
 159                 roffset += PAGE_SIZE;
 160                 len -= this_len;
 161         }
 162
 163         if (!spd.nr_pages)
 164                 return 0;
 165
 166         return wrapper_splice_to_pipe(pipe, &spd);
 167 }
 168
 169 ssize_t lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 170                                     struct pipe_inode_info *pipe, size_t len,
 171                                     unsigned int flags,
 172                                     struct lib_ring_buffer *buf)
 173 {
 174         struct channel *chan = buf->backend.chan;
 175         const struct lib_ring_buffer_config *config = &chan->backend.config;
 176         ssize_t spliced;
 177         int ret;
 178
 179         if (config->output != RING_BUFFER_SPLICE)
 180                 return -EINVAL;
 181
 182         /*
 183          * We require ppos and length to be page-aligned for performance reasons
 184          * (no page copy). Size is known using the ioctl
 185          * RING_BUFFER_GET_PADDED_SUBBUF_SIZE, which is page-size padded.
 186          * We fail when the ppos or len passed is not page-sized, because splice
 187          * is not allowed to copy more than the length passed as parameter (so
 188          * the ABI does not let us silently copy more than requested to include
 189          * padding).
 190          */
 191         if (*ppos != PAGE_ALIGN(*ppos) || len != PAGE_ALIGN(len))
 192                 return -EINVAL;
 193
 194         ret = 0;
 195         spliced = 0;
 196
 197         printk_dbg(KERN_DEBUG "SPLICE read len %zu pos %zd\n", len,
 198                    (ssize_t)*ppos);
 199         while (len && !spliced) {
 200                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, buf);
 201                 printk_dbg(KERN_DEBUG "SPLICE read loop ret %d\n", ret);
 202                 if (ret < 0)
 203                         break;
 204                 else if (!ret) {
 205                         if (flags & SPLICE_F_NONBLOCK)
 206                                 ret = -EAGAIN;
 207                         break;
 208                 }
 209
 210                 *ppos += ret;
 211                 if (ret > len)
 212                         len = 0;
 213                 else
 214                         len -= ret;
 215                 spliced += ret;
 216         }
 217
 218         if (spliced)
 219                 return spliced;
 220
 221         return ret;
 222 }
 223 EXPORT_SYMBOL_GPL(lib_ring_buffer_splice_read);
 224
 225 ssize_t vfs_lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 226                                     struct pipe_inode_info *pipe, size_t len,
 227                                     unsigned int flags)
 228 {
 229         struct lib_ring_buffer *buf = in->private_data;
 230
 231         return lib_ring_buffer_splice_read(in, ppos, pipe, len, flags, buf);
 232 }
 233 EXPORT_SYMBOL_GPL(vfs_lib_ring_buffer_splice_read);