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   8 .TH KMEM_ALLOC 9F "Oct 22, 2014"
   9 .SH NAME
  10 kmem_alloc, kmem_zalloc, kmem_free \- allocate kernel memory
  11 .SH SYNOPSIS
  12 .LP
  13 .nf
  14 #include <sys/types.h>
  15 #include <sys/kmem.h>
  16 
  17 
  18 
  19 \fBvoid *\fR\fBkmem_alloc\fR(\fBsize_t\fR \fIsize\fR, \fBint\fR \fIflag\fR);
  20 .fi
  21 
  22 .LP
  23 .nf
  24 \fBvoid *\fR\fBkmem_zalloc\fR(\fBsize_t\fR \fIsize\fR, \fBint\fR \fIflag\fR);
  25 .fi
  26 
  27 .LP
  28 .nf
  29 \fBvoid\fR \fBkmem_free\fR(\fBvoid *\fR\fIbuf\fR, \fBsize_t\fR \fIsize\fR);
  30 .fi
  31 
  32 .SH INTERFACE LEVEL
  33 .sp
  34 .LP
  35 Architecture independent level 1 (DDI/DKI).
  36 .SH PARAMETERS
  37 .sp
  38 .ne 2
  39 .na
  40 \fB\fIsize\fR\fR
  41 .ad
  42 .RS 8n
  43 Number of bytes to allocate.
  44 .RE
  45 
  46 .sp
  47 .ne 2
  48 .na
  49 \fB\fIflag\fR\fR
  50 .ad
  51 .RS 8n
  52 Determines whether caller can sleep for memory. Possible flags are
  53 \fBKM_SLEEP\fR to allow sleeping until memory is available, or \fBKM_NOSLEEP\fR
  54 to return \fINULL\fR immediately if memory is not available.
  55 .RE
  56 
  57 .sp
  58 .ne 2
  59 .na
  60 \fB\fIbuf\fR\fR
  61 .ad
  62 .RS 8n
  63 Pointer to allocated memory.
  64 .RE
  65 
  66 .SH DESCRIPTION
  67 .sp
  68 .LP
  69 The \fBkmem_alloc()\fR function allocates \fIsize\fR bytes of kernel memory and
  70 returns a pointer to the allocated memory. The allocated memory is at least
  71 double-word aligned, so it can hold any C data structure. No greater alignment
  72 can be assumed. \fIflag\fR determines whether the caller can sleep for memory.
  73 \fBKM_SLEEP\fR allocations may sleep but are guaranteed to succeed.
  74 \fBKM_NOSLEEP\fR allocations are guaranteed not to sleep but may fail (return
  75 \fINULL\fR) if no memory is currently available. The initial contents of memory
  76 allocated using \fBkmem_alloc()\fR are random garbage.
  77 .sp
  78 .LP
  79 The \fBkmem_zalloc()\fR function is like \fBkmem_alloc()\fR but returns
  80 zero-filled memory.
  81 .sp
  82 .LP
  83 The \fBkmem_free()\fR function frees previously allocated kernel memory. The
  84 buffer address and size must exactly match the original allocation. Memory
  85 cannot be returned piecemeal.
  86 .SH RETURN VALUES
  87 .sp
  88 .LP
  89 If successful, \fBkmem_alloc()\fR and \fBkmem_zalloc()\fR return a pointer to
  90 the allocated memory. If \fBKM_NOSLEEP\fR is set and memory cannot be allocated
  91 without sleeping, \fBkmem_alloc()\fR and \fBkmem_zalloc()\fR return \fINULL\fR.
  92 .SH CONTEXT
  93 .sp
  94 .LP
  95 The \fBkmem_alloc()\fR and \fBkmem_zalloc()\fR functions can be called from
  96 interrupt context only if the \fBKM_NOSLEEP\fR flag is set. They can be called
  97 from user context with any valid \fIflag\fR. The \fBkmem_free()\fR function can
  98 be called from from user, interrupt, or kernel context.
  99 .SH SEE ALSO
 100 .sp
 101 .LP
 102 \fBcopyout\fR(9F), \fBfreerbuf\fR(9F), \fBgetrbuf\fR(9F)
 103 .sp
 104 .LP
 105 \fIWriting Device Drivers\fR
 106 .SH WARNINGS
 107 .sp
 108 .LP
 109 Memory allocated using \fBkmem_alloc()\fR is not paged. Available memory is
 110 therefore limited by the total physical memory on the system. It is also
 111 limited by the available kernel virtual address space, which is often the more
 112 restrictive constraint on large-memory configurations.
 113 .sp
 114 .LP
 115 Excessive use of kernel memory is likely to affect overall system performance.
 116 Overcommitment of kernel memory will cause the system to hang or panic.
 117 .sp
 118 .LP
 119 Misuse of the kernel memory allocator, such as writing past the end of a
 120 buffer, using a buffer after freeing it, freeing a buffer twice, or freeing a
 121 null or invalid pointer, will corrupt the kernel heap and may cause the system
 122 to corrupt data or panic.
 123 .sp
 124 .LP
 125 The initial contents of memory allocated using \fBkmem_alloc()\fR are random
 126 garbage. This random garbage may include secure kernel data. Therefore,
 127 uninitialized kernel memory should be handled carefully. For example, never
 128 \fBcopyout\fR(9F) a potentially uninitialized buffer.
 129 .SH NOTES
 130 .sp
 131 .LP
 132 \fBkmem_alloc(0\fR, \fIflag\fR\fB)\fR always returns \fINULL\fR.
 133 \fBkmem_free(NULL, 0)\fR is legal.