lib/babeltrace/mmap-align.h

   1 #ifndef _BABELTRACE_MMAP_ALIGN_H
   2 #define _BABELTRACE_MMAP_ALIGN_H
   3
   4 /*
   5  * BabelTrace mmap-align.h - mmap alignment header
   6  *
   7  * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * Permission is hereby granted, free of charge, to any person obtaining a copy
  10  * of this software and associated documentation files (the "Software"), to deal
  11  * in the Software without restriction, including without limitation the rights
  12  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  13  * copies of the Software, and to permit persons to whom the Software is
  14  * furnished to do so, subject to the following conditions:
  15  *
  16  * The above copyright notice and this permission notice shall be included in
  17  * all copies or substantial portions of the Software.
  18  *
  19  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  20  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  22  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  23  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  24  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  25  * SOFTWARE.
  26  */
  27
  28 #include <babeltrace/align.h>
  29 #include <stdlib.h>
  30 #include <sys/mman.h>
  31
  32 /*
  33  * This header implements a wrapper over mmap (mmap_align) that memory
  34  * maps a file region that is not necessarily multiple of the page size.
  35  * It returns a structure (instead of a pointer) that contains the mmap
  36  * pointer (page-aligned) and a pointer to the offset requested within
  37  * that page. Note: in the current implementation, the "addr" parameter
  38  * cannot be forced, so we allocate at an address chosen by the OS.
  39  */
  40
  41 struct mmap_align {
  42         void *page_aligned_addr;        /* mmap address, aligned to floor */
  43         size_t page_aligned_length;     /* mmap length, containing range */
  44
  45         void *addr;                     /* virtual mmap address */
  46         size_t length;                  /* virtual mmap length */
  47 };
  48
  49 static inline
  50 struct mmap_align *mmap_align(size_t length, int prot,
  51                 int flags, int fd, off_t offset)
  52 {
  53         struct mmap_align *mma;
  54         off_t page_aligned_offset;      /* mmap offset, aligned to floor */
  55
  56         mma = malloc(sizeof(*mma));
  57         if (!mma)
  58                 return MAP_FAILED;
  59         mma->length = length;
  60         page_aligned_offset = ALIGN_FLOOR(offset, PAGE_SIZE);
  61         /*
  62          * Page aligned length needs to contain the requested range.
  63          * E.g., for a small range that fits within a single page, we might
  64          * require a 2 pages page_aligned_length if the range crosses a page
  65          * boundary.
  66          */
  67         mma->page_aligned_length = ALIGN(length + offset - page_aligned_offset, PAGE_SIZE);
  68         mma->page_aligned_addr = mmap(NULL, mma->page_aligned_length,
  69                 prot, flags, fd, page_aligned_offset);
  70         if (mma->page_aligned_addr == (void *) -1UL) {
  71                 free(mma);
  72                 return MAP_FAILED;
  73         }
  74         mma->addr = mma->page_aligned_addr + (offset - page_aligned_offset);
  75         return mma;
  76 }
  77
  78 static inline
  79 int munmap_align(struct mmap_align *mma)
  80 {
  81         void *page_aligned_addr;
  82         size_t page_aligned_length;
  83
  84         page_aligned_addr = mma->page_aligned_addr;
  85         page_aligned_length = mma->page_aligned_length;
  86         free(mma);
  87         return munmap(page_aligned_addr, page_aligned_length);
  88 }
  89
  90 static inline
  91 void *mmap_align_addr(struct mmap_align *mma)
  92 {
  93         return mma->addr;
  94 }
  95
  96 /*
  97  * Helper for special-cases, normally unused.
  98  */
  99 static inline
 100 void mmap_align_set_addr(struct mmap_align *mma, void *addr)
 101 {
 102         mma->addr = addr;
 103 }
 104
 105 #endif /* _BABELTRACE_MMAP_ALIGN_H */