1 BUF(9S) Data Structures for Drivers BUF(9S)
2
3
4
5 NAME
6 buf - block I/O data transfer structure
7
8 SYNOPSIS
9 #include <sys/ddi.h>
10 #include <sys/sunddi.h>
11
12
13 INTERFACE LEVEL
14 Architecture independent level 1 (DDI/DKI)
15
16 DESCRIPTION
17 The buf structure is the basic data structure for block I/O transfers.
18 Each block I/O transfer has an associated buffer header. The header
19 contains all the buffer control and status information. For drivers,
20 the buffer header pointer is the sole argument to a block driver
21 strategy(9E) routine. Do not depend on the size of the buf structure
22 when writing a driver.
23
24
25 A buffer header can be linked in multiple lists simultaneously. Because
26 of this, most of the members in the buffer header cannot be changed by
27 the driver, even when the buffer header is in one of the driver's work
28 lists.
29
30
31 Buffer headers are also used by the system for unbuffered or physical
32 I/O for block drivers. In this case, the buffer describes a portion of
33 user data space that is locked into memory.
34
35
36 Block drivers often chain block requests so that overall throughput for
37 the device is maximized. The av_forw and the av_back members of the buf
38 structure can serve as link pointers for chaining block requests.
39
40 STRUCTURE MEMBERS
41 int b_flags; /* Buffer status */
42 struct buf *av_forw; /* Driver work list link */
43 struct buf *av_back; /* Driver work list link */
44 size_t b_bcount; /* # of bytes to transfer */
45 union {
46 caddr_t b_addr; /* Buffer's virtual address */
47 } b_un;
48 daddr_t b_blkno; /* Block number on device */
49 diskaddr_t b_lblkno; /* Expanded block number on dev. */
50 size_t b_resid; /* # of bytes not xferred */
51 size_t b_bufsize; /* size of alloc. buffer */
52 int (*b_iodone)(struct buf *); /* function called */
53 /* by biodone */
54 int b_error; /* expanded error field */
55 void *b_private; /* "opaque" driver private area */
56 dev_t b_edev; /* expanded dev field */
57
58
59
60
61 The members of the buffer header available to test or set by a driver
62 are as follows:
63
64
65 b_flags stores the buffer status and indicates to the driver whether to
66 read or write to the device. The driver must never clear the b_flags
67 member. If this is done, unpredictable results can occur including loss
68 of disk sanity and the possible failure of other kernel processes.
69
70
71 All b_flags bit values not otherwise specified above are reserved by
72 the kernel and may not be used.
73
74
75 Valid flags are as follows:
76
77 B_BUSY
78 Indicates the buffer is in use. The driver must not change
79 this flag unless it allocated the buffer with getrbuf(9F)
80 and no I/O operation is in progress.
81
82
83 B_DONE
84 Indicates the data transfer has completed. This flag is
85 read-only.
86
87
88 B_ERROR
89 Indicates an I/O transfer error. It is set in conjunction
90 with the b_error field. bioerror(9F) should be used in
91 preference to setting the B_ERROR bit.
92
93
94 B_PAGEIO
95 Indicates the buffer is being used in a paged I/O request.
96 See the description of the b_un.b_addr field for more
97 information. This flag is read-only.
98
99
100 B_PHYS
101 indicates the buffer header is being used for physical
102 (direct) I/O to a user data area. See the description of
103 the b_un.b_addr field for more information. This flag is
104 read-only.
105
106
107 B_READ
108 Indicates that data is to be read from the peripheral
109 device into main memory.
110
111
112 B_WRITE
113 Indicates that the data is to be transferred from main
114 memory to the peripheral device. B_WRITE is a pseudo flag
115 and cannot be directly tested; it is only detected as the
116 NOT form of B_READ.
117
118
119
120 av_forw and av_back can be used by the driver to link the buffer into
121 driver work lists.
122
123
124 b_bcount specifies the number of bytes to be transferred in both a
125 paged and a non-paged I/O request.
126
127
128 b_un.b_addr is the virtual address of the I/O request, unless B_PAGEIO
129 is set. The address is a kernel virtual address, unless B_PHYS is set,
130 in which case it is a user virtual address. If B_PAGEIO is set,
131 b_un.b_addr contains kernel private data. Note that either one of
132 B_PHYS and B_PAGEIO, or neither, can be set, but not both.
133
134
135 b_blkno identifies which logical block on the device (the device is
136 defined by the device number) is to be accessed. The driver might have
137 to convert this logical block number to a physical location such as a
138 cylinder, track, and sector of a disk. This is a 32-bit value. The
139 driver should use b_blkno or b_lblkno, but not both.
140
141
142 b_lblkno identifies which logical block on the device (the device is
143 defined by the device number) is to be accessed. The driver might have
144 to convert this logical block number to a physical location such as a
145 cylinder, track, and sector of a disk. This is a 64-bit value. The
146 driver should use b_lblkno or b_blkno, but not both.
147
148
149 b_resid should be set to the number of bytes not transferred because of
150 an error.
151
152
153 b_bufsize contains the size of the allocated buffer.
154
155
156 b_iodone identifies a specific biodone routine to be called by the
157 driver when the I/O is complete.
158
159
160 b_error can hold an error code that should be passed as a return code
161 from the driver. b_error is set in conjunction with the B_ERROR bit set
162 in the b_flags member. bioerror(9F) should be used in preference to
163 setting the b_error field.
164
165
166 b_private is for the private use of the device driver.
167
168
169 b_edev contains the major and minor device numbers of the device
170 accessed.
171
172 SEE ALSO
173 strategy(9E), aphysio(9F), bioclone(9F), biodone(9F), bioerror(9F),
174 bioinit(9F), clrbuf(9F), getrbuf(9F), physio(9F), iovec(9S), uio(9S)
175
176
177 Writing Device Drivers
178
179 WARNINGS
180 Buffers are a shared resource within the kernel. Drivers should read or
181 write only the members listed in this section. Drivers that attempt to
182 use undocumented members of the buf structure risk corrupting data in
183 the kernel or on the device.
184
185
186
187 September 19, 2002 BUF(9S)
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1 BUF(9S) Data Structures for Drivers BUF(9S)
2
3 NAME
4 buf - block I/O data transfer structure
5
6 SYNOPSIS
7 #include <sys/ddi.h>
8 #include <sys/sunddi.h>
9
10 INTERFACE LEVEL
11 Architecture independent level 1 (DDI/DKI)
12
13 DESCRIPTION
14 The buf structure is the basic data structure for block I/O transfers.
15 Each block I/O transfer has an associated buffer header. The header
16 contains all the buffer control and status information. For drivers, the
17 buffer header pointer is the sole argument to a block driver strategy(9E)
18 routine. Do not depend on the size of the buf structure when writing a
19 driver.
20
21 A buffer header can be linked in multiple lists simultaneously. Because
22 of this, most of the members in the buffer header cannot be changed by
23 the driver, even when the buffer header is in one of the driver's work
24 lists.
25
26 Buffer headers are also used by the system for unbuffered or physical I/O
27 for block drivers. In this case, the buffer describes a portion of user
28 data space that is locked into memory.
29
30 Block drivers often chain block requests so that overall throughput for
31 the device is maximized. The av_forw and the av_back members of the buf
32 structure can serve as link pointers for chaining block requests.
33
34 STRUCTURE MEMBERS
35 int b_flags; /* Buffer status */
36 struct buf *av_forw; /* Driver work list link */
37 struct buf *av_back; /* Driver work list link */
38 size_t b_bcount; /* # of bytes to transfer */
39 union {
40 caddr_t b_addr; /* Buffer's virtual address */
41 } b_un;
42 daddr_t b_blkno; /* Block number on device */
43 diskaddr_t b_lblkno; /* Expanded block number on dev. */
44 size_t b_resid; /* # of bytes not xferred */
45 size_t b_bufsize; /* size of alloc. buffer */
46 int (*b_iodone)(struct buf *); /* function called */
47 /* by biodone */
48 int b_error; /* expanded error field */
49 void *b_private; /* "opaque" driver private area */
50 dev_t b_edev; /* expanded dev field */
51
52 The members of the buffer header available to test or set by a driver are
53 as follows:
54
55 b_flags stores the buffer status and indicates to the driver whether to
56 read or write to the device. The driver must never clear the b_flags
57 member. If this is done, unpredictable results can occur including loss
58 of disk sanity and the possible failure of other kernel processes.
59
60 All b_flags bit values not otherwise specified above are reserved by the
61 kernel and may not be used.
62
63 Valid flags are as follows:
64
65 B_BUSY Indicates the buffer is in use. The driver must not change
66 this flag unless it allocated the buffer with getrbuf(9F) and
67 no I/O operation is in progress.
68
69 B_DONE Indicates the data transfer has completed. This flag is read-
70 only.
71
72 B_ERROR Indicates an I/O transfer error. It is set in conjunction with
73 the b_error field. bioerror(9F) should be used in preference
74 to setting the B_ERROR bit.
75
76 B_PAGEIO Indicates the buffer is being used in a paged I/O request. See
77 the description of the b_un.b_addr field for more information.
78 This flag is read-only.
79
80 B_PHYS indicates the buffer header is being used for physical (direct)
81 I/O to a user data area. See the description of the
82 b_un.b_addr field for more information. This flag is read-
83 only.
84
85 B_READ Indicates that data is to be read from the peripheral device
86 into main memory.
87
88 B_WRITE Indicates that the data is to be transferred from main memory
89 to the peripheral device. B_WRITE is a pseudo flag and cannot
90 be directly tested; it is only detected as the NOT form of
91 B_READ.
92
93 av_forw and av_back can be used by the driver to link the buffer into
94 driver work lists.
95
96 b_bcount specifies the number of bytes to be transferred in both a paged
97 and a non-paged I/O request.
98
99 b_un.b_addr is the virtual address of the I/O request, unless B_PAGEIO is
100 set. The address is a kernel virtual address, unless B_PHYS is set, in
101 which case it is a user virtual address. If B_PAGEIO is set, b_un.b_addr
102 contains kernel private data. Note that either one of B_PHYS and
103 B_PAGEIO, or neither, can be set, but not both.
104
105 b_blkno identifies which logical block on the device (the device is
106 defined by the device number) is to be accessed. The driver might have
107 to convert this logical block number to a physical location such as a
108 cylinder, track, and sector of a disk. This is a 32-bit value. The
109 driver should use b_blkno or b_lblkno, but not both.
110
111 b_lblkno identifies which logical block on the device (the device is
112 defined by the device number) is to be accessed. The driver might have
113 to convert this logical block number to a physical location such as a
114 cylinder, track, and sector of a disk. This is a 64-bit value. The
115 driver should use b_lblkno or b_blkno, but not both.
116
117 b_resid should be set to the number of bytes not transferred because of
118 an error.
119
120 b_bufsize contains the size of the allocated buffer.
121
122 b_iodone identifies a specific biodone(9F) routine to be called by the
123 driver when the I/O is complete.
124
125 b_error can hold an error code that should be passed as a return code
126 from the driver. b_error is set in conjunction with the B_ERROR bit set
127 in the b_flags member. bioerror(9F) should be used in preference to
128 setting the b_error field.
129
130 b_private is for the private use of the device driver.
131
132 b_edev contains the major and minor device numbers of the device
133 accessed.
134
135 SEE ALSO
136 strategy(9E), aphysio(9F), bioclone(9F), biodone(9F), bioerror(9F),
137 bioinit(9F), clrbuf(9F), getrbuf(9F), physio(9F), iovec(9S), uio(9S)
138
139 Writing Device Drivers.
140
141 WARNINGS
142 Buffers are a shared resource within the kernel. Drivers should read or
143 write only the members listed in this section. Drivers that attempt to
144 use undocumented members of the buf structure risk corrupting data in the
145 kernel or on the device.
146
147 illumos July 9, 2018 illumos
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