12062 Convert buf(9S) to mandoc
1 .\" Copyright (c) 2002 Sun Microsystems, Inc. All Rights Reserved. 2 .\" Copyright 1989 AT&T 3 .\" The contents of this file are subject to the terms of the 4 .\" Common Development and Distribution License (the "License"). 5 .\" You may not use this file except in compliance with the License. 6 .\" 7 .\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 8 .\" or http://www.opensolaris.org/os/licensing. 9 .\" See the License for the specific language governing permissions 10 .\" and limitations under the License. 11 .\" 12 .\" When distributing Covered Code, include this CDDL HEADER in each 13 .\" file and include the License file at usr/src/OPENSOLARIS.LICENSE. 14 .\" If applicable, add the following below this CDDL HEADER, with the 15 .\" fields enclosed by brackets "[]" replaced with your own identifying 16 .\" information: Portions Copyright [yyyy] [name of copyright owner] 17 .Dd July 9, 2018 18 .Dt BUF 9S 19 .Os 20 .Sh NAME 21 .Nm buf 22 .Nd block I/O data transfer structure 23 .Sh SYNOPSIS 24 .In sys/ddi.h 25 .In sys/sunddi.h 26 .Sh INTERFACE LEVEL 27 Architecture independent level 1 (DDI/DKI) 28 .Sh DESCRIPTION 29 The 30 .Vt buf 31 structure is the basic data structure for block 32 .Sy I/O 33 transfers. 34 Each block 35 .Sy I/O 36 transfer has an associated buffer header. 37 The header contains all the buffer control and status information. 38 For drivers, the buffer header pointer is the sole argument to a block driver 39 .Xr strategy 9E 40 routine. 41 Do not depend on the size of the 42 .Vt buf 43 structure when writing a driver. 44 .Pp 45 A buffer header can be linked in multiple lists simultaneously. 46 Because of 47 this, most of the members in the buffer header cannot be changed by the driver, 48 even when the buffer header is in one of the driver's work lists. 49 .Pp 50 Buffer headers are also used by the system for unbuffered or physical 51 .Sy I/O 52 for block drivers. 53 In this case, the buffer describes a portion of user data 54 space that is locked into memory. 55 .Pp 56 Block drivers often chain block requests so that overall throughput for the 57 device is maximized. 58 The 59 .Fa av_forw 60 and the 61 .Fa av_back 62 members of the 63 .Vt buf 64 structure can serve as link pointers for chaining block requests. 65 .Sh STRUCTURE MEMBERS 66 .Bd -literal -offset 2n 67 int b_flags; /* Buffer status */ 68 struct buf *av_forw; /* Driver work list link */ 69 struct buf *av_back; /* Driver work list link */ 70 size_t b_bcount; /* # of bytes to transfer */ 71 union { 72 caddr_t b_addr; /* Buffer's virtual address */ 73 } b_un; 74 daddr_t b_blkno; /* Block number on device */ 75 diskaddr_t b_lblkno; /* Expanded block number on dev. */ 76 size_t b_resid; /* # of bytes not xferred */ 77 size_t b_bufsize; /* size of alloc. buffer */ 78 int (*b_iodone)(struct buf *); /* function called */ 79 /* by biodone */ 80 int b_error; /* expanded error field */ 81 void *b_private; /* "opaque" driver private area */ 82 dev_t b_edev; /* expanded dev field */ 83 .Ed 84 .Pp 85 The members of the buffer header available to test or set by a driver are as 86 follows: 87 .Pp 88 .Fa b_flags 89 stores the buffer status and indicates to the driver whether to 90 read or write to the device. 91 The driver must never clear the 92 .Fa b_flags 93 member. 94 If this is done, unpredictable results can occur including loss of disk 95 sanity and the possible failure of other kernel processes. 96 .Pp 97 All 98 .Fa b_flags 99 bit values not otherwise specified above are reserved by the 100 kernel and may not be used. 101 .Pp 102 Valid flags are as follows: 103 .Bl -tag -width "B_PAGEIO" 104 .It Dv B_BUSY 105 Indicates the buffer is in use. 106 The driver must not change this flag unless it allocated the buffer with 107 .Xr getrbuf 9F 108 and no 109 .Sy I/O 110 operation is in progress. 111 .It Dv B_DONE 112 Indicates the data transfer has completed. 113 This flag is read-only. 114 .It Dv B_ERROR 115 Indicates an 116 .Sy I/O 117 transfer error. 118 It is set in conjunction with the 119 .Fa b_error 120 field. 121 .Xr bioerror 9F 122 should be used in preference to setting the 123 .Dv B_ERROR 124 bit. 125 .It Dv B_PAGEIO 126 Indicates the buffer is being used in a paged 127 .Sy I/O 128 request. 129 See the description of the 130 .Fa b_un.b_addr 131 field for more information. 132 This flag is read-only. 133 .It Dv B_PHYS 134 indicates the buffer header is being used for physical (direct) 135 .Sy I/O 136 to a user data area. 137 See the description of the 138 .Fa b_un.b_addr 139 field for more information. 140 This flag is read-only. 141 .It Dv B_READ 142 Indicates that data is to be read from the peripheral device into main memory. 143 .It Dv B_WRITE 144 Indicates that the data is to be transferred from main memory to the peripheral 145 device. 146 .Dv B_WRITE 147 is a pseudo flag and cannot be directly tested; it is 148 only detected as the NOT form of 149 .Dv B_READ . 150 .El 151 .Pp 152 .Fa av_forw 153 and 154 .Fa av_back 155 can be used by the driver to link the buffer into driver work lists. 156 .Pp 157 .Fa b_bcount 158 specifies the number of bytes to be transferred in both a paged and a non-paged 159 .Sy I/O 160 request. 161 .Pp 162 .Fa b_un.b_addr 163 is the virtual address of the 164 .Sy I/O 165 request, unless 166 .Dv B_PAGEIO 167 is set. 168 The address is a kernel virtual address, unless 169 .Dv B_PHYS 170 is set, in which case it is a user virtual address. 171 If 172 .Dv B_PAGEIO 173 is set, 174 .Fa b_un.b_addr 175 contains kernel private data. 176 Note that either one of 177 .Dv B_PHYS 178 and 179 .Dv B_PAGEIO , 180 or neither, can be set, but 181 not both. 182 .Pp 183 .Fa b_blkno 184 identifies which logical block on the device (the device is 185 defined by the device number) is to be accessed. 186 The driver might have to 187 convert this logical block number to a physical location such as a cylinder, 188 track, and sector of a disk. 189 This is a 32-bit value. 190 The driver should use 191 .Fa b_blkno 192 or 193 .Fa b_lblkno , 194 but not both. 195 .Pp 196 .Fa b_lblkno 197 identifies which logical block on the device (the device is 198 defined by the device number) is to be accessed. 199 The driver might have to 200 convert this logical block number to a physical location such as a cylinder, 201 track, and sector of a disk. 202 This is a 64-bit value. 203 The driver should use 204 .Fa b_lblkno 205 or 206 .Fa b_blkno , 207 but not both. 208 .Pp 209 .Fa b_resid 210 should be set to the number of bytes not transferred because of an error. 211 .Pp 212 .Fa b_bufsize 213 contains the size of the allocated buffer. 214 .Pp 215 .Fa b_iodone 216 identifies a specific 217 .Xr biodone 9F 218 routine to be called by the driver when the 219 .Sy I/O 220 is complete. 221 .Pp 222 .Fa b_error 223 can hold an error code that should be passed as a return code 224 from the driver. 225 .Fa b_error 226 is set in conjunction with the 227 .Dv B_ERROR 228 bit 229 set in the 230 .Fa b_flags 231 member. 232 .Xr bioerror 9F 233 should be used in 234 preference to setting the 235 .Fa b_error 236 field. 237 .Pp 238 .Fa b_private 239 is for the private use of the device driver. 240 .Pp 241 .Fa b_edev 242 contains the major and minor device numbers of the device 243 accessed. 244 .Sh SEE ALSO 245 .Xr strategy 9E , 246 .Xr aphysio 9F , 247 .Xr bioclone 9F , 248 .Xr biodone 9F , 249 .Xr bioerror 9F , 250 .Xr bioinit 9F , 251 .Xr clrbuf 9F , 252 .Xr getrbuf 9F , 253 .Xr physio 9F , 254 .Xr iovec 9S , 255 .Xr uio 9S 256 .Rs 257 .%T Writing Device Drivers 258 .Re 259 .Sh WARNINGS 260 Buffers are a shared resource within the kernel. 261 Drivers should read or write only the members listed in this section. 262 Drivers that attempt to use undocumented members of the 263 .Fa buf 264 structure risk corrupting data in the kernel or on the device. --- EOF ---