contig_malloc(9r) contig_malloc(9r)
NAME
contig_malloc - General: Allocates physically contiguous memory
SYNOPSIS
#include <sys/malloc.h>
void * contig_malloc(
u_long size,
u_long alignment,
u_long addrlimit,
int type,
int flag );
ARGUMENTS
Specifies the size of the memory (in bytes) to allocate. Specifies the alignment of the memory to be allocated. For example, for a
256-byte alignment, you should pass the value 256. A 0 (zero) value means there is no alignment requirement. Specifies that the address of
all the allocated memory should be less than or equal to this address. A 0 (zero) value means that there is no address limit requirement.
Specifies the purpose for which the memory is being allocated (or freed). The memory type constants are defined in the file
/usr/sys/include/sys/malloc.h. Examples of memory type constants are M_DEVBUF (device driver memory), M_KTABLE (kernel table memory),
M_RTABLE (routing tables memory), and so forth. Specifies one of the following flags defined in /usr/sys/include/sys/malloc.h: Signifies
that contig_malloc should zero the allocated memory. Signifies that contig_malloc can block. Signifies that contig_malloc cannot block.
DESCRIPTION
The contig_malloc routine allocates physically contiguous memory during the boot process (before single-user mode). The routine carves out
an area of physically contiguous memory from a contiguous memory buffer and allocates memory from this buffer with proper alignment. The
call to contig_malloc is the same for statically or dynamically configured drivers. However, the point or points in time in which the stat-
ically or dynamically configured driver requests the memory differ.
A statically configured driver typically needs to call contig_malloc only before single-user mode. In this case, contig_malloc obtains the
memory from the contiguous memory buffer. When a statically configured driver frees this physically contiguous memory (by calling the con-
tig_free routine), the memory is returned to the virtual memory subsystem.
A dynamically configured driver typically needs physically contiguous memory after single-user mode. As stated previously, contig_malloc
carves out an area of physically contiguous memory from a contiguous memory buffer before single-user mode. Thus, this memory would not be
available to the dynamically configured driver after single-user mode. To solve this problem, a dynamically configured driver calls con-
tig_malloc by defining the CMA_Option attribute in the sysconfigtab file fragment.
The cma_dd subsystem calls contig_malloc on behalf of dynamically configured device drivers and obtains the memory allocation size (and
other information) from the CMA_Option attribute field. In this case, contig_malloc allocates physically contiguous memory from the con-
tiguous memory buffer and places it in a saved memory pool. When a dynamically configured driver needs to call contig_malloc after single-
user mode, the physically contiguous memory comes from this saved memory pool. When a dynamically configured driver frees this physically
contiguous memory (by calling the contig_free routine), the memory is returned to the saved memory pool (not to the virtual memory subsys-
tem). Thus, this physically contiguous memory is available to the dynamically configured driver upon subsequent reload requests that occur
after single-user mode.
RETURN VALUES
Upon successful completion, contig_malloc returns a pointer to the allocated memory. If contig_malloc cannot allocate the requested memory,
it returns a null pointer.
SEE ALSO
Routines: contig_free(9r)
contig_malloc(9r)