rmalloc(9F) Kernel Functions for Drivers rmalloc(9F)
NAME
rmalloc - 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
rmalloc() 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 necessary.
rmfree(9F) Return previously allocated space to a map.
rmallocmap(9F) Allocate a resource map and initialize it.
rmfreemap(9F) Deallocate a resource map.
rmalloc() allocates space from a resource map in terms of arbitrary units. The system maintains the resource map by size and index, com-
puted 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 allocated space. Otherwise, rmalloc() returns a 0 if all resource map
entries are already allocated.
CONTEXT
rmalloc() can be called from user or interrupt 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. rmallocmap(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 manage. The following example is a fragment from a hypothetical
start routine 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 routine 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 memory 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 allocated 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 request */
11 /* 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 ALSO
kmem_alloc(9F), rmalloc_wait(9F), rmallocmap(9F), rmfree(9F), rmfreemap(9F), uiomove(9F)
Writing Device Drivers
SunOS 5.10 19 Nov 1992 rmalloc(9F)