drivers/staging/lttng/lib/ringbuffer/ring_buffer_mmap.c

   1 /*
   2  * ring_buffer_mmap.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) 2008-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * Re-using content from kernel/relay.c.
   9  *
  10  * This file is released under the GPL v2.
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/mm.h>
  15
  16 #include "../../wrapper/ringbuffer/backend.h"
  17 #include "../../wrapper/ringbuffer/frontend.h"
  18 #include "../../wrapper/ringbuffer/vfs.h"
  19
  20 /*
  21  * fault() vm_op implementation for ring buffer file mapping.
  22  */
  23 static int lib_ring_buffer_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
  24 {
  25         struct lib_ring_buffer *buf = vma->vm_private_data;
  26         struct channel *chan = buf->backend.chan;
  27         const struct lib_ring_buffer_config *config = chan->backend.config;
  28         pgoff_t pgoff = vmf->pgoff;
  29         struct page **page;
  30         void **virt;
  31         unsigned long offset, sb_bindex;
  32
  33         /*
  34          * Verify that faults are only done on the range of pages owned by the
  35          * reader.
  36          */
  37         offset = pgoff << PAGE_SHIFT;
  38         sb_bindex = subbuffer_id_get_index(config, buf->backend.buf_rsb.id);
  39         if (!(offset >= buf->backend.array[sb_bindex]->mmap_offset
  40               && offset < buf->backend.array[sb_bindex]->mmap_offset +
  41                           buf->backend.chan->backend.subbuf_size))
  42                 return VM_FAULT_SIGBUS;
  43         /*
  44          * ring_buffer_read_get_page() gets the page in the current reader's
  45          * pages.
  46          */
  47         page = lib_ring_buffer_read_get_page(&buf->backend, offset, &virt);
  48         if (!*page)
  49                 return VM_FAULT_SIGBUS;
  50         get_page(*page);
  51         vmf->page = *page;
  52
  53         return 0;
  54 }
  55
  56 /*
  57  * vm_ops for ring buffer file mappings.
  58  */
  59 static const struct vm_operations_struct lib_ring_buffer_mmap_ops = {
  60         .fault = lib_ring_buffer_fault,
  61 };
  62
  63 /**
  64  *      lib_ring_buffer_mmap_buf: - mmap channel buffer to process address space
  65  *      @buf: ring buffer to map
  66  *      @vma: vm_area_struct describing memory to be mapped
  67  *
  68  *      Returns 0 if ok, negative on error
  69  *
  70  *      Caller should already have grabbed mmap_sem.
  71  */
  72 static int lib_ring_buffer_mmap_buf(struct lib_ring_buffer *buf,
  73                                     struct vm_area_struct *vma)
  74 {
  75         unsigned long length = vma->vm_end - vma->vm_start;
  76         struct channel *chan = buf->backend.chan;
  77         const struct lib_ring_buffer_config *config = chan->backend.config;
  78         unsigned long mmap_buf_len;
  79
  80         if (config->output != RING_BUFFER_MMAP)
  81                 return -EINVAL;
  82
  83         mmap_buf_len = chan->backend.buf_size;
  84         if (chan->backend.extra_reader_sb)
  85                 mmap_buf_len += chan->backend.subbuf_size;
  86
  87         if (length != mmap_buf_len)
  88                 return -EINVAL;
  89
  90         vma->vm_ops = &lib_ring_buffer_mmap_ops;
  91         vma->vm_flags |= VM_DONTEXPAND;
  92         vma->vm_private_data = buf;
  93
  94         return 0;
  95 }
  96
  97 /**
  98  *      lib_ring_buffer_mmap - mmap file op
  99  *      @filp: the file
 100  *      @vma: the vma describing what to map
 101  *
 102  *      Calls upon lib_ring_buffer_mmap_buf() to map the file into user space.
 103  */
 104 int lib_ring_buffer_mmap(struct file *filp, struct vm_area_struct *vma)
 105 {
 106         struct lib_ring_buffer *buf = filp->private_data;
 107         return lib_ring_buffer_mmap_buf(buf, vma);
 108 }
 109 EXPORT_SYMBOL_GPL(lib_ring_buffer_mmap);