RMALLOC(9F)RMALLOC(9F)NAMErmalloc - allocate space from a resource map
SYNOPSIS
#include <sys/map.h>
#include <sys/ddi.h>
unsigned long rmalloc(struct map *mp, size_t size);
INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI).
PARAMETERS
mp
Resource map from where the resource is drawn.
size
Number of units of the resource.
DESCRIPTION
The rmalloc() function is used by a driver to allocate space from a
previously defined and initialized resource map. The map itself is
allocated by calling the function rmallocmap(9F). rmalloc() is one of
five functions used for resource map management. The other functions
include:
rmalloc_wait(9F)
Allocate space from a resource map, wait if neces‐
sary.
rmfree(9F)
Return previously allocated space to a map.
rmallocmap(9F)
Allocate a resource map and initialize it.
rmfreemap(9F)
Deallocate a resource map.
The rmalloc() function allocates space from a resource map in terms of
arbitrary units. The system maintains the resource map by size and
index, computed in units appropriate for the resource. For example,
units may be byte addresses, pages of memory, or blocks. The normal
return value is an unsigned long set to the value of the index where
sufficient free space in the resource was found.
RETURN VALUES
Under normal conditions, rmalloc() returns the base index of the allo‐
cated space. Otherwise, rmalloc() returns a 0 if all resource map
entries are already allocated.
CONTEXT
The rmalloc() function can be called from user, interrupt, or kernel
context.
EXAMPLES
Example 1 Illustrating the principles of map management
The following example is a simple memory map, but it illustrates the
principles of map management. A driver allocates and initializes the
map by calling both the rmallocmap(9F) and rmfree(9F) functions. rmal‐
locmap(9F) is called to establish the number of slots or entries in the
map, and rmfree(9F) to initialize the resource area the map is to man‐
age. The following example is a fragment from a hypothetical start rou‐
tine and illustrates the following procedures:
o Panics the system if the required amount of memory can not
be allocated (lines 11-15).
o Uses rmallocmap(9F) to configure the total number of entries
in the map, and rmfree(9F) to initialize the total resource
area.
1 #define XX_MAPSIZE 12
2 #define XX_BUFSIZE 2560
3 static struct map *xx_mp; /* Private buffer space map */
...
4 xxstart()
5 /*
6 * Allocate private buffer. If insufficient memory,
7 * display message and halt system.
8 */
9 {
10 register caddr_t bp;
...
11 if ((bp = kmem_alloc(XX_BUFSIZE, KM_NOSLEEP) == 0) {
12
13 cmn_err(CE_PANIC, "xxstart: kmem_alloc failed before %d buffer"
14 "allocation", XX_BUFSIZE);
15 }
16
17 /*
18 * Initialize the resource map with number
19 * of slots in map.
20 */
21 xx_mp = rmallocmap(XX_MAPSIZE);
22
24 /*
25 * Initialize space management map with total
26 * buffer area it is to manage.
27 */
28 rmfree(xx_mp, XX_BUFSIZE, bp);
...
Example 2 Allocating buffers
The rmalloc() function is then used by the driver's read or write rou‐
tine to allocate buffers for specific data transfers. The uiomove(9F)
function is used to move the data between user space and local driver
memory. The device then moves data between itself and local driver mem‐
ory through DMA.
The next example illustrates the following procedures:
o The size of the I/O request is calculated and stored in the
size variable (line 10).
o Buffers are allocated through the rmalloc() function using
the size value (line 15). If the allocation fails the system
will panic.
o The uiomove(9F) function is used to move data to the allo‐
cated buffer (line 23).
o If the address passed to uiomove(9F) is invalid, rmfree(9F)
is called to release the previously allocated buffer, and an
EFAULT error is returned.
1 #define XX_BUFSIZE 2560
2 #define XX_MAXSIZE (XX_BUFSIZE / 4)
3
4 static struct map *xx_mp; /* Private buffer space map */
...
5 xxread(dev_t dev, uio_t *uiop, cred_t *credp)
6 {
7
8 register caddr_t addr;
9 register int size;
10 size = min(COUNT, XX_MAXSIZE); /* Break large I/O */
11 /* request into small ones */
12 /*
13 * Get buffer.
14 */
15 if ((addr = (caddr_t)rmalloc(xx_mp, size)) == 0)
16 cmn_err(CE_PANIC, "read: rmalloc failed allocation of size %d",
17 size);
18
19 /*
20 * Move data to buffer. If invalid address is found,
21 * return buffer to map and return error code.
22 */
23 if (uiomove(addr, size, UIO_READ, uiop) == -1) {
24 rmfree(xx_mp, size, addr);
25 return(EFAULT);
26 }
27 }
SEE ALSOkmem_alloc(9F), rmalloc_wait(9F), rmallocmap(9F), rmfree(9F),
rmfreemap(9F), uiomove(9F)
Writing Device Drivers
Jan 16, 2006 RMALLOC(9F)
