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