FAR void *rammap(int fd, size_t length, off_t offset)
{
FAR struct fs_rammap_s *map;
FAR uint8_t *alloc;
FAR uint8_t *rdbuffer;
ssize_t nread;
off_t fpos;
int errcode;
int ret;
/* There is a major design flaw that I have not yet thought of fix for:
* The goal is to have a single region of memory that represents a single
* file and can be shared by many threads. That is, given a filename a
* thread should be able to open the file, get a file descriptor, and
* call mmap() to get a memory region. Different file descriptors opened
* with the same file path should get the same memory region when mapped.
*
* The design flaw is that I don't have sufficient knowledge to know that
* these different file descriptors map to the same file. So, for the time
* being, a new memory region is created each time that rammap() is called.
* Not very useful!
*/
/* Allocate a region of memory of the specified size */
alloc = (FAR uint8_t *)kumm_malloc(sizeof(struct fs_rammap_s) + length);
if (!alloc)
{
ferr("ERROR: Region allocation failed, length: %d\n", (int)length);
errcode = ENOMEM;
goto errout;
}
/* Initialize the region */
map = (FAR struct fs_rammap_s *)alloc;
memset(map, 0, sizeof(struct fs_rammap_s));
map->addr = alloc + sizeof(struct fs_rammap_s);
map->length = length;
map->offset = offset;
/* Seek to the specified file offset */
fpos = lseek(fd, offset, SEEK_SET);
if (fpos == (off_t)-1)
{
/* Seek failed... errno has already been set, but EINVAL is probably
* the correct response.
*/
ferr("ERROR: Seek to position %d failed\n", (int)offset);
errcode = EINVAL;
goto errout_with_region;
}
/* Read the file data into the memory region */
rdbuffer = map->addr;
while (length > 0)
{
nread = read(fd, rdbuffer, length);
if (nread < 0)
{
/* Handle the special case where the read was interrupted by a
* signal.
*/
errcode = get_errno();
if (errcode != EINTR)
{
/* All other read errors are bad. errno is already set.
* (but maybe should be forced to EINVAL?). NOTE that if
* FS DEBUG is enabled, then the following ferr() macro will
* destroy the errno value.
*/
ferr("ERROR: Read failed: offset=%d errno=%d\n",
(int)offset, errcode);
#ifdef CONFIG_DEBUG_FS
goto errout_with_region;
#else
goto errout_with_errno;
#endif
}
}
/* Check for end of file. */
if (nread == 0)
{
break;
}
/* Increment number of bytes read */
rdbuffer += nread;
length -= nread;
}
/* Zero any memory beyond the amount read from the file */
memset(rdbuffer, 0, length);
/* Add the buffer to the list of regions */
rammap_initialize();
ret = sem_wait(&g_rammaps.exclsem);
if (ret < 0)
{
goto errout_with_errno;
}
map->flink = g_rammaps.head;
g_rammaps.head = map;
sem_post(&g_rammaps.exclsem);
return map->addr;
errout_with_region:
kumm_free(alloc);
errout:
set_errno(errcode);
return MAP_FAILED;
errout_with_errno:
kumm_free(alloc);
return MAP_FAILED;
}
int munmap(FAR void *start, size_t length)
{
FAR struct fs_rammap_s *prev;
FAR struct fs_rammap_s *curr;
FAR void *newaddr;
unsigned int offset;
int ret;
int err;
/* Find a region containing this start and length in the list of regions */
rammap_initialize();
ret = sem_wait(&g_rammaps.exclsem);
if (ret < 0)
{
return ERROR;
}
/* Seach the list of regions */
for (prev = NULL, curr = g_rammaps.head; curr; prev = curr, curr = curr->flink)
{
/* Does this region include any part of the specified range? */
if ((uintptr_t)start < (uintptr_t)curr->addr + curr->length &&
(uintptr_t)start + length >= (uintptr_t)curr->addr)
{
break;
}
}
/* Did we find the region */
if (!curr)
{
fdbg("Region not found\n");
err = EINVAL;
goto errout_with_semaphore;
}
/* Get the offset from the beginning of the region and the actual number
* of bytes to "unmap". All mappings must extend to the end of the region.
* There is no support for free a block of memory but leaving a block of
* memory at the end. This is a consequence of using kumm_realloc() to
* simulate the unmapping.
*/
offset = start - curr->addr;
if (offset + length < curr->length)
{
fdbg("Cannot umap without unmapping to the end\n");
err = ENOSYS;
goto errout_with_semaphore;
}
/* Okay.. the region is beging umapped to the end. Make sure the length
* indicates that.
*/
length = curr->length - offset;
/* Are we unmapping the entire region (offset == 0)? */
if (length >= curr->length)
{
/* Yes.. remove the mapping from the list */
if (prev)
{
prev->flink = curr->flink;
}
else
{
g_rammaps.head = curr->flink;
}
/* Then free the region */
kumm_free(curr);
}
/* No.. We have been asked to "unmap' only a portion of the memory
* (offset > 0).
*/
else
{
newaddr = kumm_realloc(curr->addr, sizeof(struct fs_rammap_s) + length);
DEBUGASSERT(newaddr == (FAR void*)(curr->addr));
curr->length = length;
}
sem_post(&g_rammaps.exclsem);
return OK;
errout_with_semaphore:
sem_post(&g_rammaps.exclsem);
set_errno(err);
return ERROR;
}
