lib/ringbuffer/ring_buffer_splice.c

   1 /* SPDX-License-Identifier: GPL-2.0-only
   2  *
   3  * ring_buffer_splice.c
   4  *
   5  * Copyright (C) 2002-2005 - Tom Zanussi <zanussi@us.ibm.com>, IBM Corp
   6  * Copyright (C) 1999-2005 - Karim Yaghmour <karim@opersys.com>
   7  * Copyright (C) 2008-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * Re-using code from kernel/relay.c, which is why it is licensed under
  10  * the GPL-2.0.
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/fs.h>
  15 #include <linux/version.h>
  16
  17 #include <wrapper/splice.h>
  18 #include <ringbuffer/backend.h>
  19 #include <ringbuffer/frontend.h>
  20 #include <ringbuffer/vfs.h>
  21
  22 #if 0
  23 #define printk_dbg(fmt, args...) printk(fmt, args)
  24 #else
  25 #define printk_dbg(fmt, args...)
  26 #endif
  27
  28 loff_t vfs_lib_ring_buffer_no_llseek(struct file *file, loff_t offset,
  29                 int origin)
  30 {
  31         return -ESPIPE;
  32 }
  33 EXPORT_SYMBOL_GPL(vfs_lib_ring_buffer_no_llseek);
  34
  35 /*
  36  * Release pages from the buffer so splice pipe_to_file can move them.
  37  * Called after the pipe has been populated with buffer pages.
  38  */
  39 static void lib_ring_buffer_pipe_buf_release(struct pipe_inode_info *pipe,
  40                                              struct pipe_buffer *pbuf)
  41 {
  42         __free_page(pbuf->page);
  43 }
  44
  45 static const struct pipe_buf_operations ring_buffer_pipe_buf_ops = {
  46 #if (LINUX_VERSION_CODE < KERNEL_VERSION(5,1,0))
  47         .can_merge = 0,
  48 #endif
  49 #if (LINUX_VERSION_CODE < KERNEL_VERSION(3,15,0))
  50         .map = generic_pipe_buf_map,
  51         .unmap = generic_pipe_buf_unmap,
  52 #endif
  53         .confirm = generic_pipe_buf_confirm,
  54         .release = lib_ring_buffer_pipe_buf_release,
  55         .steal = generic_pipe_buf_steal,
  56         .get = generic_pipe_buf_get,
  57 };
  58
  59 /*
  60  * Page release operation after splice pipe_to_file ends.
  61  */
  62 static void lib_ring_buffer_page_release(struct splice_pipe_desc *spd,
  63                                          unsigned int i)
  64 {
  65         __free_page(spd->pages[i]);
  66 }
  67
  68 /*
  69  *      subbuf_splice_actor - splice up to one subbuf's worth of data
  70  */
  71 static int subbuf_splice_actor(struct file *in,
  72                                loff_t *ppos,
  73                                struct pipe_inode_info *pipe,
  74                                size_t len,
  75                                unsigned int flags,
  76                                struct lib_ring_buffer *buf)
  77 {
  78         struct channel *chan = buf->backend.chan;
  79         const struct lib_ring_buffer_config *config = &chan->backend.config;
  80         unsigned int poff, subbuf_pages, nr_pages;
  81         struct page *pages[PIPE_DEF_BUFFERS];
  82         struct partial_page partial[PIPE_DEF_BUFFERS];
  83         struct splice_pipe_desc spd = {
  84                 .pages = pages,
  85                 .nr_pages = 0,
  86                 .partial = partial,
  87 #if (LINUX_VERSION_CODE < KERNEL_VERSION(4,12,0))
  88                 .flags = flags,
  89 #endif
  90                 .ops = &ring_buffer_pipe_buf_ops,
  91                 .spd_release = lib_ring_buffer_page_release,
  92         };
  93         unsigned long consumed_old, roffset;
  94         unsigned long bytes_avail;
  95
  96         /*
  97          * Check that a GET_SUBBUF ioctl has been done before.
  98          */
  99         WARN_ON(atomic_long_read(&buf->active_readers) != 1);
 100         consumed_old = lib_ring_buffer_get_consumed(config, buf);
 101         consumed_old += *ppos;
 102
 103         /*
 104          * Adjust read len, if longer than what is available.
 105          * Max read size is 1 subbuffer due to get_subbuf/put_subbuf for
 106          * protection.
 107          */
 108         bytes_avail = chan->backend.subbuf_size;
 109         WARN_ON(bytes_avail > chan->backend.buf_size);
 110         len = min_t(size_t, len, bytes_avail);
 111         subbuf_pages = bytes_avail >> PAGE_SHIFT;
 112         nr_pages = min_t(unsigned int, subbuf_pages, PIPE_DEF_BUFFERS);
 113         roffset = consumed_old & PAGE_MASK;
 114         poff = consumed_old & ~PAGE_MASK;
 115         printk_dbg(KERN_DEBUG "SPLICE actor len %zu pos %zd write_pos %ld\n",
 116                    len, (ssize_t)*ppos, lib_ring_buffer_get_offset(config, buf));
 117
 118         for (; spd.nr_pages < nr_pages; spd.nr_pages++) {
 119                 unsigned int this_len;
 120                 unsigned long *pfnp, new_pfn;
 121                 struct page *new_page;
 122                 void **virt;
 123
 124                 if (!len)
 125                         break;
 126                 printk_dbg(KERN_DEBUG "SPLICE actor loop len %zu roffset %ld\n",
 127                            len, roffset);
 128
 129                 /*
 130                  * We have to replace the page we are moving into the splice
 131                  * pipe.
 132                  */
 133                 new_page = alloc_pages_node(cpu_to_node(max(buf->backend.cpu,
 134                                                             0)),
 135                                             GFP_KERNEL | __GFP_ZERO, 0);
 136                 if (!new_page)
 137                         break;
 138                 new_pfn = page_to_pfn(new_page);
 139                 this_len = PAGE_SIZE - poff;
 140                 pfnp = lib_ring_buffer_read_get_pfn(&buf->backend, roffset, &virt);
 141                 spd.pages[spd.nr_pages] = pfn_to_page(*pfnp);
 142                 *pfnp = new_pfn;
 143                 *virt = page_address(new_page);
 144                 spd.partial[spd.nr_pages].offset = poff;
 145                 spd.partial[spd.nr_pages].len = this_len;
 146
 147                 poff = 0;
 148                 roffset += PAGE_SIZE;
 149                 len -= this_len;
 150         }
 151
 152         if (!spd.nr_pages)
 153                 return 0;
 154
 155         return wrapper_splice_to_pipe(pipe, &spd);
 156 }
 157
 158 ssize_t lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 159                                     struct pipe_inode_info *pipe, size_t len,
 160                                     unsigned int flags,
 161                                     struct lib_ring_buffer *buf)
 162 {
 163         struct channel *chan = buf->backend.chan;
 164         const struct lib_ring_buffer_config *config = &chan->backend.config;
 165         ssize_t spliced;
 166         int ret;
 167
 168         if (config->output != RING_BUFFER_SPLICE)
 169                 return -EINVAL;
 170
 171         /*
 172          * We require ppos and length to be page-aligned for performance reasons
 173          * (no page copy). Size is known using the ioctl
 174          * RING_BUFFER_GET_PADDED_SUBBUF_SIZE, which is page-size padded.
 175          * We fail when the ppos or len passed is not page-sized, because splice
 176          * is not allowed to copy more than the length passed as parameter (so
 177          * the ABI does not let us silently copy more than requested to include
 178          * padding).
 179          */
 180         if (*ppos != PAGE_ALIGN(*ppos) || len != PAGE_ALIGN(len))
 181                 return -EINVAL;
 182
 183         ret = 0;
 184         spliced = 0;
 185
 186         printk_dbg(KERN_DEBUG "SPLICE read len %zu pos %zd\n", len,
 187                    (ssize_t)*ppos);
 188         while (len && !spliced) {
 189                 ret = subbuf_splice_actor(in, ppos, pipe, len, flags, buf);
 190                 printk_dbg(KERN_DEBUG "SPLICE read loop ret %d\n", ret);
 191                 if (ret < 0)
 192                         break;
 193                 else if (!ret) {
 194                         if (flags & SPLICE_F_NONBLOCK)
 195                                 ret = -EAGAIN;
 196                         break;
 197                 }
 198
 199                 *ppos += ret;
 200                 if (ret > len)
 201                         len = 0;
 202                 else
 203                         len -= ret;
 204                 spliced += ret;
 205         }
 206
 207         if (spliced)
 208                 return spliced;
 209
 210         return ret;
 211 }
 212 EXPORT_SYMBOL_GPL(lib_ring_buffer_splice_read);
 213
 214 ssize_t vfs_lib_ring_buffer_splice_read(struct file *in, loff_t *ppos,
 215                                     struct pipe_inode_info *pipe, size_t len,
 216                                     unsigned int flags)
 217 {
 218         struct lib_ring_buffer *buf = in->private_data;
 219
 220         return lib_ring_buffer_splice_read(in, ppos, pipe, len, flags, buf);
 221 }
 222 EXPORT_SYMBOL_GPL(vfs_lib_ring_buffer_splice_read);