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 #if (LINUX_VERSION_CODE < KERNEL_VERSION(5,1,0))
  60         .can_merge = 0,
  61 #endif
  62 #if (LINUX_VERSION_CODE < KERNEL_VERSION(3,15,0))
  63         .map = generic_pipe_buf_map,
  64         .unmap = generic_pipe_buf_unmap,
  65 #endif
  66         .confirm = generic_pipe_buf_confirm,
  67         .release = lib_ring_buffer_pipe_buf_release,
  68         .steal = generic_pipe_buf_steal,
  69         .get = generic_pipe_buf_get,
  70 };
  71
  72 /*
  73  * Page release operation after splice pipe_to_file ends.
  74  */
  75 static void lib_ring_buffer_page_release(struct splice_pipe_desc *spd,
  76                                          unsigned int i)
  77 {
  78         __free_page(spd->pages[i]);
  79 }
  80
  81 /*
  82  *      subbuf_splice_actor - splice up to one subbuf's worth of data
  83  */
  84 static int subbuf_splice_actor(struct file *in,
  85                                loff_t *ppos,
  86                                struct pipe_inode_info *pipe,
  87                                size_t len,
  88                                unsigned int flags,
  89                                struct lib_ring_buffer *buf)
  90 {
  91         struct channel *chan = buf->backend.chan;
  92         const struct lib_ring_buffer_config *config = &chan->backend.config;
  93         unsigned int poff, subbuf_pages, nr_pages;
  94         struct page *pages[PIPE_DEF_BUFFERS];
  95         struct partial_page partial[PIPE_DEF_BUFFERS];
  96         struct splice_pipe_desc spd = {
  97                 .pages = pages,
  98                 .nr_pages = 0,
  99                 .partial = partial,
 100 #if (LINUX_VERSION_CODE < KERNEL_VERSION(4,12,0))
 101                 .flags = flags,
 102 #endif
 103                 .ops = &ring_buffer_pipe_buf_ops,
 104                 .spd_release = lib_ring_buffer_page_release,
 105         };
 106         unsigned long consumed_old, roffset;
 107         unsigned long bytes_avail;
 108
 109         /*
 110          * Check that a GET_SUBBUF ioctl has been done before.
 111          */
 112         WARN_ON(atomic_long_read(&buf->active_readers) != 1);
 113         consumed_old = lib_ring_buffer_get_consumed(config, buf);
 114         consumed_old += *ppos;
 115
 116         /*
 117          * Adjust read len, if longer than what is available.
 118          * Max read size is 1 subbuffer due to get_subbuf/put_subbuf for
 119          * protection.
 120          */
 121         bytes_avail = chan->backend.subbuf_size;
 122         WARN_ON(bytes_avail > chan->backend.buf_size);
 123         len = min_t(size_t, len, bytes_avail);
 124         subbuf_pages = bytes_avail >> PAGE_SHIFT;
 125         nr_pages = min_t(unsigned int, subbuf_pages, PIPE_DEF_BUFFERS);
 126         roffset = consumed_old & PAGE_MASK;
 127         poff = consumed_old & ~PAGE_MASK;
 128         printk_dbg(KERN_DEBUG "SPLICE actor len %zu pos %zd write_pos %ld\n",
 129                    len, (ssize_t)*ppos, lib_ring_buffer_get_offset(config, buf));
 130
 131         for (; spd.nr_pages < nr_pages; spd.nr_pages++) {
 132                 unsigned int this_len;
 133                 unsigned long *pfnp, new_pfn;
 134                 struct page *new_page;
 135                 void **virt;
 136
 137                 if (!len)
 138                         break;
 139                 printk_dbg(KERN_DEBUG "SPLICE actor loop len %zu roffset %ld\n",
 140                            len, roffset);
 141
 142                 /*
 143                  * We have to replace the page we are moving into the splice
 144                  * pipe.
 145                  */
 146                 new_page = alloc_pages_node(cpu_to_node(max(buf->backend.cpu,
 147                                                             0)),
 148                                             GFP_KERNEL | __GFP_ZERO, 0);
 149                 if (!new_page)
 150                         break;
 151                 new_pfn = page_to_pfn(new_page);
 152                 this_len = PAGE_SIZE - poff;
 153                 pfnp = lib_ring_buffer_read_get_pfn(&buf->backend, roffset, &virt);
 154                 spd.pages[spd.nr_pages] = pfn_to_page(*pfnp);
 155                 *pfnp = new_pfn;
 156                 *virt = page_address(new_page);
 157                 spd.partial[spd.nr_pages].offset = poff;
 158                 spd.partial[spd.nr_pages].len = this_len;
 159
 160                 poff = 0;
 161                 roffset += PAGE_SIZE;
 162                 len -= this_len;
 163         }
 164
 165         if (!spd.nr_pages)
 166                 return 0;
 167
 168         return wrapper_splice_to_pipe(pipe, &spd);
 169 }
 170
 171 ssize_t lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 172                                     struct pipe_inode_info *pipe, size_t len,
 173                                     unsigned int flags,
 174                                     struct lib_ring_buffer *buf)
 175 {
 176         struct channel *chan = buf->backend.chan;
 177         const struct lib_ring_buffer_config *config = &chan->backend.config;
 178         ssize_t spliced;
 179         int ret;
 180
 181         if (config->output != RING_BUFFER_SPLICE)
 182                 return -EINVAL;
 183
 184         /*
 185          * We require ppos and length to be page-aligned for performance reasons
 186          * (no page copy). Size is known using the ioctl
 187          * RING_BUFFER_GET_PADDED_SUBBUF_SIZE, which is page-size padded.
 188          * We fail when the ppos or len passed is not page-sized, because splice
 189          * is not allowed to copy more than the length passed as parameter (so
 190          * the ABI does not let us silently copy more than requested to include
 191          * padding).
 192          */
 193         if (*ppos != PAGE_ALIGN(*ppos) || len != PAGE_ALIGN(len))
 194                 return -EINVAL;
 195
 196         ret = 0;
 197         spliced = 0;
 198
 199         printk_dbg(KERN_DEBUG "SPLICE read len %zu pos %zd\n", len,
 200                    (ssize_t)*ppos);
 201         while (len && !spliced) {
 202                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, buf);
 203                 printk_dbg(KERN_DEBUG "SPLICE read loop ret %d\n", ret);
 204                 if (ret < 0)
 205                         break;
 206                 else if (!ret) {
 207                         if (flags & SPLICE_F_NONBLOCK)
 208                                 ret = -EAGAIN;
 209                         break;
 210                 }
 211
 212                 *ppos += ret;
 213                 if (ret > len)
 214                         len = 0;
 215                 else
 216                         len -= ret;
 217                 spliced += ret;
 218         }
 219
 220         if (spliced)
 221                 return spliced;
 222
 223         return ret;
 224 }
 225 EXPORT_SYMBOL_GPL(lib_ring_buffer_splice_read);
 226
 227 ssize_t vfs_lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 228                                     struct pipe_inode_info *pipe, size_t len,
 229                                     unsigned int flags)
 230 {
 231         struct lib_ring_buffer *buf = in->private_data;
 232
 233         return lib_ring_buffer_splice_read(in, ppos, pipe, len, flags, buf);
 234 }
 235 EXPORT_SYMBOL_GPL(vfs_lib_ring_buffer_splice_read);