lib/ringbuffer/ring_buffer_mmap.c

   1 /* SPDX-License-Identifier: GPL-2.0-only
   2  *
   3  * ring_buffer_mmap.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, hence the GPL-2.0-only license for this
  10  * file.
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/mm.h>
  15
  16 #include <ringbuffer/backend.h>
  17 #include <ringbuffer/frontend.h>
  18 #include <ringbuffer/vfs.h>
  19
  20 /*
  21  * fault() vm_op implementation for ring buffer file mapping.
  22  */
  23 static vm_fault_t lib_ring_buffer_fault_compat(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         unsigned long *pfnp;
  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_pfn() gets the page frame number for the
  45          * current reader's pages.
  46          */
  47         pfnp = lib_ring_buffer_read_get_pfn(&buf->backend, offset, &virt);
  48         if (!*pfnp)
  49                 return VM_FAULT_SIGBUS;
  50         get_page(pfn_to_page(*pfnp));
  51         vmf->page = pfn_to_page(*pfnp);
  52
  53         return 0;
  54 }
  55
  56 static vm_fault_t lib_ring_buffer_fault(struct vm_fault *vmf)
  57 {
  58         struct vm_area_struct *vma = vmf->vma;
  59         return lib_ring_buffer_fault_compat(vma, vmf);
  60 }
  61
  62 /*
  63  * vm_ops for ring buffer file mappings.
  64  */
  65 static const struct vm_operations_struct lib_ring_buffer_mmap_ops = {
  66         .fault = lib_ring_buffer_fault,
  67 };
  68
  69 /**
  70  *      lib_ring_buffer_mmap_buf: - mmap channel buffer to process address space
  71  *      @buf: ring buffer to map
  72  *      @vma: vm_area_struct describing memory to be mapped
  73  *
  74  *      Returns 0 if ok, negative on error
  75  *
  76  *      Caller should already have grabbed mmap_sem.
  77  */
  78 static int lib_ring_buffer_mmap_buf(struct lib_ring_buffer *buf,
  79                                     struct vm_area_struct *vma)
  80 {
  81         unsigned long length = vma->vm_end - vma->vm_start;
  82         struct channel *chan = buf->backend.chan;
  83         const struct lib_ring_buffer_config *config = &chan->backend.config;
  84         unsigned long mmap_buf_len;
  85
  86         if (config->output != RING_BUFFER_MMAP)
  87                 return -EINVAL;
  88
  89         mmap_buf_len = chan->backend.buf_size;
  90         if (chan->backend.extra_reader_sb)
  91                 mmap_buf_len += chan->backend.subbuf_size;
  92
  93         if (length != mmap_buf_len)
  94                 return -EINVAL;
  95
  96         vma->vm_ops = &lib_ring_buffer_mmap_ops;
  97         vma->vm_flags |= VM_DONTEXPAND;
  98         vma->vm_private_data = buf;
  99
 100         return 0;
 101 }
 102
 103 int lib_ring_buffer_mmap(struct file *filp, struct vm_area_struct *vma,
 104                 struct lib_ring_buffer *buf)
 105 {
 106         return lib_ring_buffer_mmap_buf(buf, vma);
 107 }
 108 EXPORT_SYMBOL_GPL(lib_ring_buffer_mmap);
 109
 110 /**
 111  *      vfs_lib_ring_buffer_mmap - mmap file op
 112  *      @filp: the file
 113  *      @vma: the vma describing what to map
 114  *
 115  *      Calls upon lib_ring_buffer_mmap_buf() to map the file into user space.
 116  */
 117 int vfs_lib_ring_buffer_mmap(struct file *filp, struct vm_area_struct *vma)
 118 {
 119         struct lib_ring_buffer *buf = filp->private_data;
 120         return lib_ring_buffer_mmap(filp, vma, buf);
 121 }
 122 EXPORT_SYMBOL_GPL(vfs_lib_ring_buffer_mmap);