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   8 .TH KMEM_ALLOC 9F "Nov 20, 2019"
   9 .SH NAME
  10 kmem_alloc, kmem_zalloc, kmem_free \- allocate kernel memory
  11 .SH SYNOPSIS
  12 .nf
  13 #include <sys/types.h>
  14 #include <sys/kmem.h>
  15 
  16 
  17 
  18 \fBvoid *\fR\fBkmem_alloc\fR(\fBsize_t\fR \fIsize\fR, \fBint\fR \fIflag\fR);
  19 .fi
  20 
  21 .LP
  22 .nf
  23 \fBvoid *\fR\fBkmem_zalloc\fR(\fBsize_t\fR \fIsize\fR, \fBint\fR \fIflag\fR);
  24 .fi
  25 
  26 .LP
  27 .nf
  28 \fBvoid\fR \fBkmem_free\fR(\fBvoid *\fR\fIbuf\fR, \fBsize_t\fR \fIsize\fR);
  29 .fi
  30 
  31 .SH INTERFACE LEVEL
  32 Architecture independent level 1 (DDI/DKI).
  33 .SH PARAMETERS
  34 .ne 2
  35 .na
  36 \fB\fIsize\fR\fR
  37 .ad
  38 .RS 8n
  39 Number of bytes to allocate.
  40 .RE
  41 
  42 .sp
  43 .ne 2
  44 .na
  45 \fB\fIflag\fR\fR
  46 .ad
  47 .RS 8n
  48 Determines whether caller can sleep for memory. Possible flags are
  49 \fBKM_SLEEP\fR to allow sleeping until memory is available, or \fBKM_NOSLEEP\fR
  50 to return \fINULL\fR immediately if memory is not available.
  51 .RE
  52 
  53 .sp
  54 .ne 2
  55 .na
  56 \fB\fIbuf\fR\fR
  57 .ad
  58 .RS 8n
  59 Pointer to allocated memory.
  60 .RE
  61 
  62 .SH DESCRIPTION
  63 The \fBkmem_alloc()\fR function allocates \fIsize\fR bytes of kernel memory and
  64 returns a pointer to the allocated memory. The allocated memory is at least
  65 double-word aligned, so it can hold any C data structure. No greater alignment
  66 can be assumed. \fIflag\fR determines whether the caller can sleep for memory.
  67 \fBKM_SLEEP\fR allocations may sleep but are guaranteed to succeed.
  68 \fBKM_NOSLEEP\fR allocations are guaranteed not to sleep but may fail (return
  69 \fINULL\fR) if no memory is currently available. The initial contents of memory
  70 allocated using \fBkmem_alloc()\fR are random garbage.
  71 .sp
  72 .LP
  73 The \fBkmem_zalloc()\fR function is like \fBkmem_alloc()\fR but returns
  74 zero-filled memory.
  75 .sp
  76 .LP
  77 The \fBkmem_free()\fR function frees previously allocated kernel memory. The
  78 buffer address and size must exactly match the original allocation. Memory
  79 cannot be returned piecemeal.
  80 .SH RETURN VALUES
  81 If successful, \fBkmem_alloc()\fR and \fBkmem_zalloc()\fR return a pointer to
  82 the allocated memory. If \fBKM_NOSLEEP\fR is set and memory cannot be allocated
  83 without sleeping, \fBkmem_alloc()\fR and \fBkmem_zalloc()\fR return \fINULL\fR.
  84 .SH CONTEXT
  85 The \fBkmem_alloc()\fR and \fBkmem_zalloc()\fR functions can be called from
  86 interrupt context only if the \fBKM_NOSLEEP\fR flag is set. They can be called
  87 from user context with any valid \fIflag\fR. The \fBkmem_free()\fR function can
  88 be called from from user, interrupt, or kernel context.
  89 .SH SEE ALSO
  90 \fBcopyout\fR(9F), \fBfreerbuf\fR(9F), \fBgetrbuf\fR(9F)
  91 .sp
  92 .LP
  93 \fIWriting Device Drivers\fR
  94 .SH WARNINGS
  95 Memory allocated using \fBkmem_alloc()\fR is not paged. Available memory is
  96 therefore limited by the total physical memory on the system. It is also
  97 limited by the available kernel virtual address space, which is often the more
  98 restrictive constraint on large-memory configurations.
  99 .sp
 100 .LP
 101 Excessive use of kernel memory is likely to affect overall system performance.
 102 Overcommitment of kernel memory will cause the system to hang or panic.
 103 .sp
 104 .LP
 105 Misuse of the kernel memory allocator, such as writing past the end of a
 106 buffer, using a buffer after freeing it, freeing a buffer twice, or freeing a
 107 null or invalid pointer, will corrupt the kernel heap and may cause the system
 108 to corrupt data or panic.
 109 .sp
 110 .LP
 111 The initial contents of memory allocated using \fBkmem_alloc()\fR are random
 112 garbage. This random garbage may include secure kernel data. Therefore,
 113 uninitialized kernel memory should be handled carefully. For example, never
 114 \fBcopyout\fR(9F) a potentially uninitialized buffer.
 115 .SH NOTES
 116 \fBkmem_alloc(0\fR, \fIflag\fR\fB)\fR always returns \fINULL\fR, but
 117 if \fBKM_SLEEP\fR is set, this behavior is considered to be deprecated;
 118 the system may be configured to explicitly panic in this case in lieu
 119 of returning \fINULL\fR.
 120 \fBkmem_free(NULL, 0)\fR is legal, however.