Based on kernel version 4.15. Page generated on 2018-01-29 10:00 EST.
1 ========================================= 2 How to get printk format specifiers right 3 ========================================= 4 5 :Author: Randy Dunlap <rdunlap@infradead.org> 6 :Author: Andrew Murray <amurray@mpc-data.co.uk> 7 8 Integer types 9 ============= 10 11 :: 12 13 If variable is of Type, use printk format specifier: 14 ------------------------------------------------------------ 15 int %d or %x 16 unsigned int %u or %x 17 long %ld or %lx 18 unsigned long %lu or %lx 19 long long %lld or %llx 20 unsigned long long %llu or %llx 21 size_t %zu or %zx 22 ssize_t %zd or %zx 23 s32 %d or %x 24 u32 %u or %x 25 s64 %lld or %llx 26 u64 %llu or %llx 27 28 If <type> is dependent on a config option for its size (e.g., ``sector_t``, 29 ``blkcnt_t``) or is architecture-dependent for its size (e.g., ``tcflag_t``), 30 use a format specifier of its largest possible type and explicitly cast to it. 31 32 Example:: 33 34 printk("test: sector number/total blocks: %llu/%llu\n", 35 (unsigned long long)sector, (unsigned long long)blockcount); 36 37 Reminder: ``sizeof()`` result is of type ``size_t``. 38 39 The kernel's printf does not support ``%n``. For obvious reasons, floating 40 point formats (``%e, %f, %g, %a``) are also not recognized. Use of any 41 unsupported specifier or length qualifier results in a WARN and early 42 return from vsnprintf. 43 44 Raw pointer value SHOULD be printed with %p. The kernel supports 45 the following extended format specifiers for pointer types: 46 47 Pointer Types 48 ============= 49 50 Pointers printed without a specifier extension (i.e unadorned %p) are 51 hashed to give a unique identifier without leaking kernel addresses to user 52 space. On 64 bit machines the first 32 bits are zeroed. If you _really_ 53 want the address see %px below. 54 55 :: 56 57 %p abcdef12 or 00000000abcdef12 58 59 Symbols/Function Pointers 60 ========================= 61 62 :: 63 64 %pF versatile_init+0x0/0x110 65 %pf versatile_init 66 %pS versatile_init+0x0/0x110 67 %pSR versatile_init+0x9/0x110 68 (with __builtin_extract_return_addr() translation) 69 %ps versatile_init 70 %pB prev_fn_of_versatile_init+0x88/0x88 71 72 The ``F`` and ``f`` specifiers are for printing function pointers, 73 for example, f->func, &gettimeofday. They have the same result as 74 ``S`` and ``s`` specifiers. But they do an extra conversion on 75 ia64, ppc64 and parisc64 architectures where the function pointers 76 are actually function descriptors. 77 78 The ``S`` and ``s`` specifiers can be used for printing symbols 79 from direct addresses, for example, __builtin_return_address(0), 80 (void *)regs->ip. They result in the symbol name with (``S``) or 81 without (``s``) offsets. If KALLSYMS are disabled then the symbol 82 address is printed instead. 83 84 The ``B`` specifier results in the symbol name with offsets and should be 85 used when printing stack backtraces. The specifier takes into 86 consideration the effect of compiler optimisations which may occur 87 when tail-call``s are used and marked with the noreturn GCC attribute. 88 89 Examples:: 90 91 printk("Going to call: %pF\n", gettimeofday); 92 printk("Going to call: %pF\n", p->func); 93 printk("%s: called from %pS\n", __func__, (void *)_RET_IP_); 94 printk("%s: called from %pS\n", __func__, 95 (void *)__builtin_return_address(0)); 96 printk("Faulted at %pS\n", (void *)regs->ip); 97 printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack); 98 99 Kernel Pointers 100 =============== 101 102 :: 103 104 %pK 01234567 or 0123456789abcdef 105 106 For printing kernel pointers which should be hidden from unprivileged 107 users. The behaviour of ``%pK`` depends on the ``kptr_restrict sysctl`` - see 108 Documentation/sysctl/kernel.txt for more details. 109 110 Unmodified Addresses 111 ==================== 112 113 :: 114 115 %px 01234567 or 0123456789abcdef 116 117 For printing pointers when you _really_ want to print the address. Please 118 consider whether or not you are leaking sensitive information about the 119 Kernel layout in memory before printing pointers with %px. %px is 120 functionally equivalent to %lx. %px is preferred to %lx because it is more 121 uniquely grep'able. If, in the future, we need to modify the way the Kernel 122 handles printing pointers it will be nice to be able to find the call 123 sites. 124 125 Struct Resources 126 ================ 127 128 :: 129 130 %pr [mem 0x60000000-0x6fffffff flags 0x2200] or 131 [mem 0x0000000060000000-0x000000006fffffff flags 0x2200] 132 %pR [mem 0x60000000-0x6fffffff pref] or 133 [mem 0x0000000060000000-0x000000006fffffff pref] 134 135 For printing struct resources. The ``R`` and ``r`` specifiers result in a 136 printed resource with (``R``) or without (``r``) a decoded flags member. 137 Passed by reference. 138 139 Physical addresses types ``phys_addr_t`` 140 ======================================== 141 142 :: 143 144 %pa[p] 0x01234567 or 0x0123456789abcdef 145 146 For printing a ``phys_addr_t`` type (and its derivatives, such as 147 ``resource_size_t``) which can vary based on build options, regardless of 148 the width of the CPU data path. Passed by reference. 149 150 DMA addresses types ``dma_addr_t`` 151 ================================== 152 153 :: 154 155 %pad 0x01234567 or 0x0123456789abcdef 156 157 For printing a ``dma_addr_t`` type which can vary based on build options, 158 regardless of the width of the CPU data path. Passed by reference. 159 160 Raw buffer as an escaped string 161 =============================== 162 163 :: 164 165 %*pE[achnops] 166 167 For printing raw buffer as an escaped string. For the following buffer:: 168 169 1b 62 20 5c 43 07 22 90 0d 5d 170 171 few examples show how the conversion would be done (the result string 172 without surrounding quotes):: 173 174 %*pE "\eb \C\a"\220\r]" 175 %*pEhp "\x1bb \C\x07"\x90\x0d]" 176 %*pEa "\e\142\040\\\103\a\042\220\r\135" 177 178 The conversion rules are applied according to an optional combination 179 of flags (see :c:func:`string_escape_mem` kernel documentation for the 180 details): 181 182 - ``a`` - ESCAPE_ANY 183 - ``c`` - ESCAPE_SPECIAL 184 - ``h`` - ESCAPE_HEX 185 - ``n`` - ESCAPE_NULL 186 - ``o`` - ESCAPE_OCTAL 187 - ``p`` - ESCAPE_NP 188 - ``s`` - ESCAPE_SPACE 189 190 By default ESCAPE_ANY_NP is used. 191 192 ESCAPE_ANY_NP is the sane choice for many cases, in particularly for 193 printing SSIDs. 194 195 If field width is omitted the 1 byte only will be escaped. 196 197 Raw buffer as a hex string 198 ========================== 199 200 :: 201 202 %*ph 00 01 02 ... 3f 203 %*phC 00:01:02: ... :3f 204 %*phD 00-01-02- ... -3f 205 %*phN 000102 ... 3f 206 207 For printing a small buffers (up to 64 bytes long) as a hex string with 208 certain separator. For the larger buffers consider to use 209 :c:func:`print_hex_dump`. 210 211 MAC/FDDI addresses 212 ================== 213 214 :: 215 216 %pM 00:01:02:03:04:05 217 %pMR 05:04:03:02:01:00 218 %pMF 00-01-02-03-04-05 219 %pm 000102030405 220 %pmR 050403020100 221 222 For printing 6-byte MAC/FDDI addresses in hex notation. The ``M`` and ``m`` 223 specifiers result in a printed address with (``M``) or without (``m``) byte 224 separators. The default byte separator is the colon (``:``). 225 226 Where FDDI addresses are concerned the ``F`` specifier can be used after 227 the ``M`` specifier to use dash (``-``) separators instead of the default 228 separator. 229 230 For Bluetooth addresses the ``R`` specifier shall be used after the ``M`` 231 specifier to use reversed byte order suitable for visual interpretation 232 of Bluetooth addresses which are in the little endian order. 233 234 Passed by reference. 235 236 IPv4 addresses 237 ============== 238 239 :: 240 241 %pI4 1.2.3.4 242 %pi4 001.002.003.004 243 %p[Ii]4[hnbl] 244 245 For printing IPv4 dot-separated decimal addresses. The ``I4`` and ``i4`` 246 specifiers result in a printed address with (``i4``) or without (``I4``) 247 leading zeros. 248 249 The additional ``h``, ``n``, ``b``, and ``l`` specifiers are used to specify 250 host, network, big or little endian order addresses respectively. Where 251 no specifier is provided the default network/big endian order is used. 252 253 Passed by reference. 254 255 IPv6 addresses 256 ============== 257 258 :: 259 260 %pI6 0001:0002:0003:0004:0005:0006:0007:0008 261 %pi6 00010002000300040005000600070008 262 %pI6c 1:2:3:4:5:6:7:8 263 264 For printing IPv6 network-order 16-bit hex addresses. The ``I6`` and ``i6`` 265 specifiers result in a printed address with (``I6``) or without (``i6``) 266 colon-separators. Leading zeros are always used. 267 268 The additional ``c`` specifier can be used with the ``I`` specifier to 269 print a compressed IPv6 address as described by 270 http://tools.ietf.org/html/rfc5952 271 272 Passed by reference. 273 274 IPv4/IPv6 addresses (generic, with port, flowinfo, scope) 275 ========================================================= 276 277 :: 278 279 %pIS 1.2.3.4 or 0001:0002:0003:0004:0005:0006:0007:0008 280 %piS 001.002.003.004 or 00010002000300040005000600070008 281 %pISc 1.2.3.4 or 1:2:3:4:5:6:7:8 282 %pISpc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345 283 %p[Ii]S[pfschnbl] 284 285 For printing an IP address without the need to distinguish whether it``s 286 of type AF_INET or AF_INET6, a pointer to a valid ``struct sockaddr``, 287 specified through ``IS`` or ``iS``, can be passed to this format specifier. 288 289 The additional ``p``, ``f``, and ``s`` specifiers are used to specify port 290 (IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ``:`` prefix, 291 flowinfo a ``/`` and scope a ``%``, each followed by the actual value. 292 293 In case of an IPv6 address the compressed IPv6 address as described by 294 http://tools.ietf.org/html/rfc5952 is being used if the additional 295 specifier ``c`` is given. The IPv6 address is surrounded by ``[``, ``]`` in 296 case of additional specifiers ``p``, ``f`` or ``s`` as suggested by 297 https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07 298 299 In case of IPv4 addresses, the additional ``h``, ``n``, ``b``, and ``l`` 300 specifiers can be used as well and are ignored in case of an IPv6 301 address. 302 303 Passed by reference. 304 305 Further examples:: 306 307 %pISfc 1.2.3.4 or [1:2:3:4:5:6:7:8]/123456789 308 %pISsc 1.2.3.4 or [1:2:3:4:5:6:7:8]%1234567890 309 %pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789 310 311 UUID/GUID addresses 312 =================== 313 314 :: 315 316 %pUb 00010203-0405-0607-0809-0a0b0c0d0e0f 317 %pUB 00010203-0405-0607-0809-0A0B0C0D0E0F 318 %pUl 03020100-0504-0706-0809-0a0b0c0e0e0f 319 %pUL 03020100-0504-0706-0809-0A0B0C0E0E0F 320 321 For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L', 322 'b' and 'B' specifiers are used to specify a little endian order in 323 lower ('l') or upper case ('L') hex characters - and big endian order 324 in lower ('b') or upper case ('B') hex characters. 325 326 Where no additional specifiers are used the default big endian 327 order with lower case hex characters will be printed. 328 329 Passed by reference. 330 331 dentry names 332 ============ 333 334 :: 335 336 %pd{,2,3,4} 337 %pD{,2,3,4} 338 339 For printing dentry name; if we race with :c:func:`d_move`, the name might be 340 a mix of old and new ones, but it won't oops. ``%pd`` dentry is a safer 341 equivalent of ``%s`` ``dentry->d_name.name`` we used to use, ``%pd<n>`` prints 342 ``n`` last components. ``%pD`` does the same thing for struct file. 343 344 Passed by reference. 345 346 block_device names 347 ================== 348 349 :: 350 351 %pg sda, sda1 or loop0p1 352 353 For printing name of block_device pointers. 354 355 struct va_format 356 ================ 357 358 :: 359 360 %pV 361 362 For printing struct va_format structures. These contain a format string 363 and va_list as follows:: 364 365 struct va_format { 366 const char *fmt; 367 va_list *va; 368 }; 369 370 Implements a "recursive vsnprintf". 371 372 Do not use this feature without some mechanism to verify the 373 correctness of the format string and va_list arguments. 374 375 Passed by reference. 376 377 kobjects 378 ======== 379 380 :: 381 382 %pO 383 384 Base specifier for kobject based structs. Must be followed with 385 character for specific type of kobject as listed below: 386 387 Device tree nodes: 388 389 %pOF[fnpPcCF] 390 391 For printing device tree nodes. The optional arguments are: 392 f device node full_name 393 n device node name 394 p device node phandle 395 P device node path spec (name + @unit) 396 F device node flags 397 c major compatible string 398 C full compatible string 399 Without any arguments prints full_name (same as %pOFf) 400 The separator when using multiple arguments is ':' 401 402 Examples: 403 404 %pOF /foo/bar@0 - Node full name 405 %pOFf /foo/bar@0 - Same as above 406 %pOFfp /foo/bar@0:10 - Node full name + phandle 407 %pOFfcF /foo/bar@0:foo,device:--P- - Node full name + 408 major compatible string + 409 node flags 410 D - dynamic 411 d - detached 412 P - Populated 413 B - Populated bus 414 415 Passed by reference. 416 417 418 struct clk 419 ========== 420 421 :: 422 423 %pC pll1 424 %pCn pll1 425 %pCr 1560000000 426 427 For printing struct clk structures. ``%pC`` and ``%pCn`` print the name 428 (Common Clock Framework) or address (legacy clock framework) of the 429 structure; ``%pCr`` prints the current clock rate. 430 431 Passed by reference. 432 433 bitmap and its derivatives such as cpumask and nodemask 434 ======================================================= 435 436 :: 437 438 %*pb 0779 439 %*pbl 0,3-6,8-10 440 441 For printing bitmap and its derivatives such as cpumask and nodemask, 442 ``%*pb`` output the bitmap with field width as the number of bits and ``%*pbl`` 443 output the bitmap as range list with field width as the number of bits. 444 445 Passed by reference. 446 447 Flags bitfields such as page flags, gfp_flags 448 ============================================= 449 450 :: 451 452 %pGp referenced|uptodate|lru|active|private 453 %pGg GFP_USER|GFP_DMA32|GFP_NOWARN 454 %pGv read|exec|mayread|maywrite|mayexec|denywrite 455 456 For printing flags bitfields as a collection of symbolic constants that 457 would construct the value. The type of flags is given by the third 458 character. Currently supported are [p]age flags, [v]ma_flags (both 459 expect ``unsigned long *``) and [g]fp_flags (expects ``gfp_t *``). The flag 460 names and print order depends on the particular type. 461 462 Note that this format should not be used directly in :c:func:`TP_printk()` part 463 of a tracepoint. Instead, use the ``show_*_flags()`` functions from 464 <trace/events/mmflags.h>. 465 466 Passed by reference. 467 468 Network device features 469 ======================= 470 471 :: 472 473 %pNF 0x000000000000c000 474 475 For printing netdev_features_t. 476 477 Passed by reference. 478 479 If you add other ``%p`` extensions, please extend lib/test_printf.c with 480 one or more test cases, if at all feasible. 481 482 483 Thank you for your cooperation and attention.