'\" te
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.TH DDI_UMEM_ALLOC 9F "Mar 19, 2002"
.SH NAME
ddi_umem_alloc, ddi_umem_free \- allocate and free page-aligned kernel memory
.SH SYNOPSIS
.nf
#include <sys/types.h>
#include <sys/sunddi.h>

\fBvoid *\fR\fBddi_umem_alloc\fR(\fBsize_t\fR \fIsize\fR, \fBint\fR \fIflag\fR,
     \fBddi_umem_cookie_t *\fR\fIcookiep\fR);
.fi

.LP
.nf
\fBvoid\fR \fBddi_umem_free\fR(\fBddi_umem_cookie_t\fR \fIcookie\fR);
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI).
.SH PARAMETERS
.SS "ddi_umem_alloc()"
.ne 2
.na
\fB\fIsize\fR\fR
.ad
.RS 11n
Number of bytes to allocate.
.RE

.sp
.ne 2
.na
\fB\fIflag\fR\fR
.ad
.RS 11n
Used to determine the sleep and pageable conditions.
.sp
Possible sleep flags are \fBDDI_UMEM_SLEEP\fR, which allows sleeping until
memory is available, and \fBDDI_UMEM_NOSLEEP\fR, which returns \fBNULL\fR
immediately if memory is not available.
.sp
The default condition is to allocate locked memory; this can be changed to
allocate pageable memory using the \fBDDI_UMEM_PAGEABLE\fR flag.
.RE

.sp
.ne 2
.na
\fB\fIcookiep\fR\fR
.ad
.RS 11n
Pointer to a kernel memory cookie.
.RE

.SS "ddi_umem_free()"
.ne 2
.na
\fB\fIcookie\fR\fR
.ad
.RS 10n
A kernel memory cookie allocated in \fBddi_umem_alloc()\fR.
.RE

.SH DESCRIPTION
\fBddi_umem_alloc()\fR allocates page-aligned kernel memory and returns a
pointer to the allocated memory. The number of bytes allocated is a multiple of
the system page size (roundup of \fIsize\fR). The allocated memory can be used
in the kernel and can be exported to user space. See \fBdevmap\fR(9E) and
\fBdevmap_umem_setup\fR(9F) for further information.
.sp
.LP
\fIflag\fR determines whether the caller can sleep for memory and whether the
allocated memory is locked or not. \fBDDI_UMEM_SLEEP\fR allocations may sleep
but are guaranteed to succeed. \fBDDI_UMEM_NOSLEEP\fR allocations do not sleep
but may fail (return \fINULL\fR) if memory is currently unavailable. If
\fBDDI_UMEM_PAGEABLE\fR is set, pageable memory will be allocated. These pages
can be swapped out to secondary memory devices. The initial contents of memory
allocated using \fBddi_umem_alloc()\fR is zero-filled.
.sp
.LP
\fI*cookiep\fR is a pointer to the kernel memory cookie that describes the
kernel memory being allocated. A typical use of \fIcookiep\fR is in
\fBdevmap_umem_setup\fR(9F) when the drivers want to export the kernel memory
to a user application.
.sp
.LP
To free the allocated memory, a driver calls \fBddi_umem_free()\fR with the
cookie obtained from \fBddi_umem_alloc()\fR. \fBddi_umem_free()\fR releases the
entire buffer.
.SH RETURN VALUES
.ne 2
.na
\fB\fBNon-null\fR\fR
.ad
.RS 12n
Successful completion. \fBddi_umem_alloc()\fR returns a pointer to the
allocated memory.
.RE

.sp
.ne 2
.na
\fB\fBNULL\fR\fR
.ad
.RS 12n
Memory cannot be allocated by \fBddi_umem_alloc()\fR because
\fBDDI_UMEM_NOSLEEP\fR is set and the system is out of resources.
.RE

.SH CONTEXT
\fBddi_umem_alloc()\fR can be called from any context if \fIflag\fR is set to
\fBDDI_UMEM_NOSLEEP.\fR If \fBDDI_UMEM_SLEEP\fR is set, \fBddi_umem_alloc()\fR
can be called from user and kernel context only. \fBddi_umem_free()\fR can be
called from any context.
.SH SEE ALSO
\fBdevmap\fR(9E), \fBcondvar\fR(9F), \fBdevmap_umem_setup\fR(9F),
\fBkmem_alloc\fR(9F), \fBmutex\fR(9F), \fBrwlock\fR(9F), \fBsemaphore\fR(9F)
.sp
.LP
\fIWriting Device Drivers\fR
.SH WARNINGS
Setting the \fBDDI_UMEM_PAGEABLE\fR flag in \fBddi_umem_alloc()\fR will result
in an allocation of pageable memory. Because these pages can be swapped out to
secondary memory devices, drivers should use this flag with care. This memory
must not be used for the following purposes:
.RS +4
.TP
.ie t \(bu
.el o
For synchronization objects such as locks and condition variables. See
\fBmutex\fR(9F), \fBsemaphore\fR(9F), \fBrwlock\fR(9F), and \fBcondvar\fR(9F).
.RE
.RS +4
.TP
.ie t \(bu
.el o
For driver interrupt routines.
.RE
.sp
.LP
Memory allocated using \fBddi_umem_alloc()\fR without setting
\fBDDI_UMEM_PAGEABLE\fR flag cannot be paged. Available memory is therefore
limited by the total physical memory on the system. It is also limited by the
available kernel virtual address space, which is often the more restrictive
constraint on large-memory configurations.
.sp
.LP
Excessive use of kernel memory is likely to effect overall system performance.
Over-commitment of kernel memory may cause unpredictable consequences.
.sp
.LP
Misuse of the kernel memory allocator, such as writing past the end of a
buffer, using a buffer after freeing it, freeing a buffer twice, or freeing an
invalid pointer, will cause the system to corrupt data or panic.
.sp
.LP
Do not call \fBddi_umem_alloc()\fR within \fBDDI_SUSPEND\fR and
\fBDDI_RESUME\fR operations. Memory acquired at these times is not reliable. In
some cases, such a call can cause a system to hang.
.SH NOTES
\fBddi_umem_alloc(0,\fR \fIflag\fR, \fIcookiep\fR\fB)\fR always returns
\fBNULL.\fR \fBddi_umem_free(NULL)\fR has no effects on system.