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11927 Log, or optionally panic, on zero-length kmem allocations
Reviewed by: Dan McDonald <danmcd@joyent.com>
Reviewed by: Jason King <jason.brian.king@gmail.com>
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--- old/usr/src/man/man9f/kmem_alloc.9f
+++ new/usr/src/man/man9f/kmem_alloc.9f
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8 -.TH KMEM_ALLOC 9F "Oct 22, 2014"
8 +.TH KMEM_ALLOC 9F "Nov 20, 2019"
9 9 .SH NAME
10 10 kmem_alloc, kmem_zalloc, kmem_free \- allocate kernel memory
11 11 .SH SYNOPSIS
12 -.LP
13 12 .nf
14 13 #include <sys/types.h>
15 14 #include <sys/kmem.h>
16 15
17 16
18 17
19 18 \fBvoid *\fR\fBkmem_alloc\fR(\fBsize_t\fR \fIsize\fR, \fBint\fR \fIflag\fR);
20 19 .fi
21 20
22 21 .LP
23 22 .nf
24 23 \fBvoid *\fR\fBkmem_zalloc\fR(\fBsize_t\fR \fIsize\fR, \fBint\fR \fIflag\fR);
25 24 .fi
26 25
27 26 .LP
28 27 .nf
29 28 \fBvoid\fR \fBkmem_free\fR(\fBvoid *\fR\fIbuf\fR, \fBsize_t\fR \fIsize\fR);
30 29 .fi
31 30
32 31 .SH INTERFACE LEVEL
33 -.sp
34 -.LP
35 32 Architecture independent level 1 (DDI/DKI).
36 33 .SH PARAMETERS
37 -.sp
38 34 .ne 2
39 35 .na
40 36 \fB\fIsize\fR\fR
41 37 .ad
42 38 .RS 8n
43 39 Number of bytes to allocate.
44 40 .RE
45 41
46 42 .sp
47 43 .ne 2
48 44 .na
49 45 \fB\fIflag\fR\fR
50 46 .ad
51 47 .RS 8n
52 48 Determines whether caller can sleep for memory. Possible flags are
53 49 \fBKM_SLEEP\fR to allow sleeping until memory is available, or \fBKM_NOSLEEP\fR
54 50 to return \fINULL\fR immediately if memory is not available.
55 51 .RE
56 52
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57 53 .sp
58 54 .ne 2
59 55 .na
60 56 \fB\fIbuf\fR\fR
61 57 .ad
62 58 .RS 8n
63 59 Pointer to allocated memory.
64 60 .RE
65 61
66 62 .SH DESCRIPTION
67 -.sp
68 -.LP
69 63 The \fBkmem_alloc()\fR function allocates \fIsize\fR bytes of kernel memory and
70 64 returns a pointer to the allocated memory. The allocated memory is at least
71 65 double-word aligned, so it can hold any C data structure. No greater alignment
72 66 can be assumed. \fIflag\fR determines whether the caller can sleep for memory.
73 67 \fBKM_SLEEP\fR allocations may sleep but are guaranteed to succeed.
74 68 \fBKM_NOSLEEP\fR allocations are guaranteed not to sleep but may fail (return
75 69 \fINULL\fR) if no memory is currently available. The initial contents of memory
76 70 allocated using \fBkmem_alloc()\fR are random garbage.
77 71 .sp
78 72 .LP
79 73 The \fBkmem_zalloc()\fR function is like \fBkmem_alloc()\fR but returns
80 74 zero-filled memory.
81 75 .sp
82 76 .LP
83 77 The \fBkmem_free()\fR function frees previously allocated kernel memory. The
84 78 buffer address and size must exactly match the original allocation. Memory
85 79 cannot be returned piecemeal.
86 80 .SH RETURN VALUES
87 -.sp
88 -.LP
89 81 If successful, \fBkmem_alloc()\fR and \fBkmem_zalloc()\fR return a pointer to
90 82 the allocated memory. If \fBKM_NOSLEEP\fR is set and memory cannot be allocated
91 83 without sleeping, \fBkmem_alloc()\fR and \fBkmem_zalloc()\fR return \fINULL\fR.
92 84 .SH CONTEXT
93 -.sp
94 -.LP
95 85 The \fBkmem_alloc()\fR and \fBkmem_zalloc()\fR functions can be called from
96 86 interrupt context only if the \fBKM_NOSLEEP\fR flag is set. They can be called
97 87 from user context with any valid \fIflag\fR. The \fBkmem_free()\fR function can
98 88 be called from from user, interrupt, or kernel context.
99 89 .SH SEE ALSO
100 -.sp
101 -.LP
102 90 \fBcopyout\fR(9F), \fBfreerbuf\fR(9F), \fBgetrbuf\fR(9F)
103 91 .sp
104 92 .LP
105 93 \fIWriting Device Drivers\fR
106 94 .SH WARNINGS
107 -.sp
108 -.LP
109 95 Memory allocated using \fBkmem_alloc()\fR is not paged. Available memory is
110 96 therefore limited by the total physical memory on the system. It is also
111 97 limited by the available kernel virtual address space, which is often the more
112 98 restrictive constraint on large-memory configurations.
113 99 .sp
114 100 .LP
115 101 Excessive use of kernel memory is likely to affect overall system performance.
116 102 Overcommitment of kernel memory will cause the system to hang or panic.
117 103 .sp
118 104 .LP
119 105 Misuse of the kernel memory allocator, such as writing past the end of a
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120 106 buffer, using a buffer after freeing it, freeing a buffer twice, or freeing a
121 107 null or invalid pointer, will corrupt the kernel heap and may cause the system
122 108 to corrupt data or panic.
123 109 .sp
124 110 .LP
125 111 The initial contents of memory allocated using \fBkmem_alloc()\fR are random
126 112 garbage. This random garbage may include secure kernel data. Therefore,
127 113 uninitialized kernel memory should be handled carefully. For example, never
128 114 \fBcopyout\fR(9F) a potentially uninitialized buffer.
129 115 .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.
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.
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