1 /* 2 * linux/include/linux/console.h 3 * 4 * Copyright (C) 1993 Hamish Macdonald 5 * 6 * This file is subject to the terms and conditions of the GNU General Public 7 * License. See the file COPYING in the main directory of this archive 8 * for more details. 9 * 10 * Changed: 11 * 10-Mar-94: Arno Griffioen: Conversion for vt100 emulator port from PC LINUX 12 */ 13 14 #ifndef _LINUX_CONSOLE_H_ 15 #define _LINUX_CONSOLE_H_ 1 16 17 #include <linux/atomic.h> 18 #include <linux/bits.h> 19 #include <linux/irq_work.h> 20 #include <linux/rculist.h> 21 #include <linux/rcuwait.h> 22 #include <linux/smp.h> 23 #include <linux/types.h> 24 #include <linux/vesa.h> 25 26 struct vc_data; 27 struct console_font_op; 28 struct console_font; 29 struct module; 30 struct tty_struct; 31 struct notifier_block; 32 33 enum con_scroll { 34 SM_UP, 35 SM_DOWN, 36 }; 37 38 enum vc_intensity; 39 40 /** 41 * struct consw - callbacks for consoles 42 * 43 * @owner: the module to get references of when this console is used 44 * @con_startup: set up the console and return its name (like VGA, EGA, ...) 45 * @con_init: initialize the console on @vc. @init is true for the very first 46 * call on this @vc. 47 * @con_deinit: deinitialize the console from @vc. 48 * @con_clear: erase @count characters at [@x, @y] on @vc. @count >= 1. 49 * @con_putc: emit one character with attributes @ca to [@x, @y] on @vc. 50 * (optional -- @con_putcs would be called instead) 51 * @con_putcs: emit @count characters with attributes @s to [@x, @y] on @vc. 52 * @con_cursor: enable/disable cursor depending on @enable 53 * @con_scroll: move lines from @top to @bottom in direction @dir by @lines. 54 * Return true if no generic handling should be done. 55 * Invoked by csi_M and printing to the console. 56 * @con_switch: notifier about the console switch; it is supposed to return 57 * true if a redraw is needed. 58 * @con_blank: blank/unblank the console. The target mode is passed in @blank. 59 * @mode_switch is set if changing from/to text/graphics. The hook 60 * is supposed to return true if a redraw is needed. 61 * @con_font_set: set console @vc font to @font with height @vpitch. @flags can 62 * be %KD_FONT_FLAG_DONT_RECALC. (optional) 63 * @con_font_get: fetch the current font on @vc of height @vpitch into @font. 64 * (optional) 65 * @con_font_default: set default font on @vc. @name can be %NULL or font name 66 * to search for. @font can be filled back. (optional) 67 * @con_resize: resize the @vc console to @width x @height. @from_user is true 68 * when this change comes from the user space. 69 * @con_set_palette: sets the palette of the console @vc to @table (optional) 70 * @con_scrolldelta: the contents of the console should be scrolled by @lines. 71 * Invoked by user. (optional) 72 * @con_set_origin: set origin (see &vc_data::vc_origin) of the @vc. If not 73 * provided or returns false, the origin is set to 74 * @vc->vc_screenbuf. (optional) 75 * @con_save_screen: save screen content into @vc->vc_screenbuf. Called e.g. 76 * upon entering graphics. (optional) 77 * @con_build_attr: build attributes based on @color, @intensity and other 78 * parameters. The result is used for both normal and erase 79 * characters. (optional) 80 * @con_invert_region: invert a region of length @count on @vc starting at @p. 81 * (optional) 82 */ 83 struct consw { 84 struct module *owner; 85 const char *(*con_startup)(void); 86 void (*con_init)(struct vc_data *vc, bool init); 87 void (*con_deinit)(struct vc_data *vc); 88 void (*con_clear)(struct vc_data *vc, unsigned int y, 89 unsigned int x, unsigned int count); 90 void (*con_putc)(struct vc_data *vc, u16 ca, unsigned int y, 91 unsigned int x); 92 void (*con_putcs)(struct vc_data *vc, const u16 *s, 93 unsigned int count, unsigned int ypos, 94 unsigned int xpos); 95 void (*con_cursor)(struct vc_data *vc, bool enable); 96 bool (*con_scroll)(struct vc_data *vc, unsigned int top, 97 unsigned int bottom, enum con_scroll dir, 98 unsigned int lines); 99 bool (*con_switch)(struct vc_data *vc); 100 bool (*con_blank)(struct vc_data *vc, enum vesa_blank_mode blank, 101 bool mode_switch); 102 int (*con_font_set)(struct vc_data *vc, 103 const struct console_font *font, 104 unsigned int vpitch, unsigned int flags); 105 int (*con_font_get)(struct vc_data *vc, struct console_font *font, 106 unsigned int vpitch); 107 int (*con_font_default)(struct vc_data *vc, 108 struct console_font *font, const char *name); 109 int (*con_resize)(struct vc_data *vc, unsigned int width, 110 unsigned int height, bool from_user); 111 void (*con_set_palette)(struct vc_data *vc, 112 const unsigned char *table); 113 void (*con_scrolldelta)(struct vc_data *vc, int lines); 114 bool (*con_set_origin)(struct vc_data *vc); 115 void (*con_save_screen)(struct vc_data *vc); 116 u8 (*con_build_attr)(struct vc_data *vc, u8 color, 117 enum vc_intensity intensity, 118 bool blink, bool underline, bool reverse, bool italic); 119 void (*con_invert_region)(struct vc_data *vc, u16 *p, int count); 120 }; 121 122 extern const struct consw *conswitchp; 123 124 extern const struct consw dummy_con; /* dummy console buffer */ 125 extern const struct consw vga_con; /* VGA text console */ 126 extern const struct consw newport_con; /* SGI Newport console */ 127 128 struct screen_info; 129 #ifdef CONFIG_VGA_CONSOLE 130 void vgacon_register_screen(struct screen_info *si); 131 #else 132 static inline void vgacon_register_screen(struct screen_info *si) { } 133 #endif 134 135 int con_is_bound(const struct consw *csw); 136 int do_unregister_con_driver(const struct consw *csw); 137 int do_take_over_console(const struct consw *sw, int first, int last, int deflt); 138 void give_up_console(const struct consw *sw); 139 #ifdef CONFIG_VT 140 void con_debug_enter(struct vc_data *vc); 141 void con_debug_leave(void); 142 #else 143 static inline void con_debug_enter(struct vc_data *vc) { } 144 static inline void con_debug_leave(void) { } 145 #endif 146 147 /* 148 * The interface for a console, or any other device that wants to capture 149 * console messages (printer driver?) 150 */ 151 152 /** 153 * enum cons_flags - General console flags 154 * @CON_PRINTBUFFER: Used by newly registered consoles to avoid duplicate 155 * output of messages that were already shown by boot 156 * consoles or read by userspace via syslog() syscall. 157 * @CON_CONSDEV: Indicates that the console driver is backing 158 * /dev/console. 159 * @CON_ENABLED: Indicates if a console is allowed to print records. If 160 * false, the console also will not advance to later 161 * records. 162 * @CON_BOOT: Marks the console driver as early console driver which 163 * is used during boot before the real driver becomes 164 * available. It will be automatically unregistered 165 * when the real console driver is registered unless 166 * "keep_bootcon" parameter is used. 167 * @CON_ANYTIME: A misnomed historical flag which tells the core code 168 * that the legacy @console::write callback can be invoked 169 * on a CPU which is marked OFFLINE. That is misleading as 170 * it suggests that there is no contextual limit for 171 * invoking the callback. The original motivation was 172 * readiness of the per-CPU areas. 173 * @CON_BRL: Indicates a braille device which is exempt from 174 * receiving the printk spam for obvious reasons. 175 * @CON_EXTENDED: The console supports the extended output format of 176 * /dev/kmesg which requires a larger output buffer. 177 * @CON_SUSPENDED: Indicates if a console is suspended. If true, the 178 * printing callbacks must not be called. 179 * @CON_NBCON: Console can operate outside of the legacy style console_lock 180 * constraints. 181 * @CON_NBCON_ATOMIC_UNSAFE: The write_atomic() callback is not safe and is 182 * therefore only used by nbcon_atomic_flush_unsafe(). 183 */ 184 enum cons_flags { 185 CON_PRINTBUFFER = BIT(0), 186 CON_CONSDEV = BIT(1), 187 CON_ENABLED = BIT(2), 188 CON_BOOT = BIT(3), 189 CON_ANYTIME = BIT(4), 190 CON_BRL = BIT(5), 191 CON_EXTENDED = BIT(6), 192 CON_SUSPENDED = BIT(7), 193 CON_NBCON = BIT(8), 194 CON_NBCON_ATOMIC_UNSAFE = BIT(9), 195 }; 196 197 /** 198 * struct nbcon_state - console state for nbcon consoles 199 * @atom: Compound of the state fields for atomic operations 200 * 201 * @req_prio: The priority of a handover request 202 * @prio: The priority of the current owner 203 * @unsafe: Console is busy in a non takeover region 204 * @unsafe_takeover: A hostile takeover in an unsafe state happened in the 205 * past. The console cannot be safe until re-initialized. 206 * @cpu: The CPU on which the owner runs 207 * 208 * To be used for reading and preparing of the value stored in the nbcon 209 * state variable @console::nbcon_state. 210 * 211 * The @prio and @req_prio fields are particularly important to allow 212 * spin-waiting to timeout and give up without the risk of a waiter being 213 * assigned the lock after giving up. 214 */ 215 struct nbcon_state { 216 union { 217 unsigned int atom; 218 struct { 219 unsigned int prio : 2; 220 unsigned int req_prio : 2; 221 unsigned int unsafe : 1; 222 unsigned int unsafe_takeover : 1; 223 unsigned int cpu : 24; 224 }; 225 }; 226 }; 227 228 /* 229 * The nbcon_state struct is used to easily create and interpret values that 230 * are stored in the @console::nbcon_state variable. Ensure this struct stays 231 * within the size boundaries of the atomic variable's underlying type in 232 * order to avoid any accidental truncation. 233 */ 234 static_assert(sizeof(struct nbcon_state) <= sizeof(int)); 235 236 /** 237 * enum nbcon_prio - console owner priority for nbcon consoles 238 * @NBCON_PRIO_NONE: Unused 239 * @NBCON_PRIO_NORMAL: Normal (non-emergency) usage 240 * @NBCON_PRIO_EMERGENCY: Emergency output (WARN/OOPS...) 241 * @NBCON_PRIO_PANIC: Panic output 242 * @NBCON_PRIO_MAX: The number of priority levels 243 * 244 * A higher priority context can takeover the console when it is 245 * in the safe state. The final attempt to flush consoles in panic() 246 * can be allowed to do so even in an unsafe state (Hope and pray). 247 */ 248 enum nbcon_prio { 249 NBCON_PRIO_NONE = 0, 250 NBCON_PRIO_NORMAL, 251 NBCON_PRIO_EMERGENCY, 252 NBCON_PRIO_PANIC, 253 NBCON_PRIO_MAX, 254 }; 255 256 struct console; 257 struct printk_buffers; 258 259 /** 260 * struct nbcon_context - Context for console acquire/release 261 * @console: The associated console 262 * @spinwait_max_us: Limit for spin-wait acquire 263 * @prio: Priority of the context 264 * @allow_unsafe_takeover: Allow performing takeover even if unsafe. Can 265 * be used only with NBCON_PRIO_PANIC @prio. It 266 * might cause a system freeze when the console 267 * is used later. 268 * @backlog: Ringbuffer has pending records 269 * @pbufs: Pointer to the text buffer for this context 270 * @seq: The sequence number to print for this context 271 */ 272 struct nbcon_context { 273 /* members set by caller */ 274 struct console *console; 275 unsigned int spinwait_max_us; 276 enum nbcon_prio prio; 277 unsigned int allow_unsafe_takeover : 1; 278 279 /* members set by emit */ 280 unsigned int backlog : 1; 281 282 /* members set by acquire */ 283 struct printk_buffers *pbufs; 284 u64 seq; 285 }; 286 287 /** 288 * struct nbcon_write_context - Context handed to the nbcon write callbacks 289 * @ctxt: The core console context 290 * @outbuf: Pointer to the text buffer for output 291 * @len: Length to write 292 * @unsafe_takeover: If a hostile takeover in an unsafe state has occurred 293 * @cpu: CPU on which the message was generated 294 * @pid: PID of the task that generated the message 295 * @comm: Name of the task that generated the message 296 */ 297 struct nbcon_write_context { 298 struct nbcon_context __private ctxt; 299 char *outbuf; 300 unsigned int len; 301 bool unsafe_takeover; 302 #ifdef CONFIG_PRINTK_EXECUTION_CTX 303 int cpu; 304 pid_t pid; 305 char comm[TASK_COMM_LEN]; 306 #endif 307 }; 308 309 /** 310 * struct console - The console descriptor structure 311 * @name: The name of the console driver 312 * @write: Legacy write callback to output messages (Optional) 313 * @read: Read callback for console input (Optional) 314 * @device: The underlying TTY device driver (Optional) 315 * @unblank: Callback to unblank the console (Optional) 316 * @setup: Callback for initializing the console (Optional) 317 * @exit: Callback for teardown of the console (Optional) 318 * @match: Callback for matching a console (Optional) 319 * @flags: Console flags. See enum cons_flags 320 * @index: Console index, e.g. port number 321 * @cflag: TTY control mode flags 322 * @ispeed: TTY input speed 323 * @ospeed: TTY output speed 324 * @seq: Sequence number of the next ringbuffer record to print 325 * @dropped: Number of unreported dropped ringbuffer records 326 * @data: Driver private data 327 * @node: hlist node for the console list 328 * 329 * @nbcon_state: State for nbcon consoles 330 * @nbcon_seq: Sequence number of the next record for nbcon to print 331 * @nbcon_device_ctxt: Context available for non-printing operations 332 * @nbcon_prev_seq: Seq num the previous nbcon owner was assigned to print 333 * @pbufs: Pointer to nbcon private buffer 334 * @kthread: Printer kthread for this console 335 * @rcuwait: RCU-safe wait object for @kthread waking 336 * @irq_work: Defer @kthread waking to IRQ work context 337 */ 338 struct console { 339 char name[16]; 340 void (*write)(struct console *co, const char *s, unsigned int count); 341 int (*read)(struct console *co, char *s, unsigned int count); 342 struct tty_driver *(*device)(struct console *co, int *index); 343 void (*unblank)(void); 344 int (*setup)(struct console *co, char *options); 345 int (*exit)(struct console *co); 346 int (*match)(struct console *co, char *name, int idx, char *options); 347 short flags; 348 short index; 349 int cflag; 350 uint ispeed; 351 uint ospeed; 352 u64 seq; 353 unsigned long dropped; 354 void *data; 355 struct hlist_node node; 356 357 /* nbcon console specific members */ 358 359 /** 360 * @write_atomic: 361 * 362 * NBCON callback to write out text in any context. (Optional) 363 * 364 * This callback is called with the console already acquired. However, 365 * a higher priority context is allowed to take it over by default. 366 * 367 * The callback must call nbcon_enter_unsafe() and nbcon_exit_unsafe() 368 * around any code where the takeover is not safe, for example, when 369 * manipulating the serial port registers. 370 * 371 * nbcon_enter_unsafe() will fail if the context has lost the console 372 * ownership in the meantime. In this case, the callback is no longer 373 * allowed to go forward. It must back out immediately and carefully. 374 * The buffer content is also no longer trusted since it no longer 375 * belongs to the context. 376 * 377 * The callback should allow the takeover whenever it is safe. It 378 * increases the chance to see messages when the system is in trouble. 379 * If the driver must reacquire ownership in order to finalize or 380 * revert hardware changes, nbcon_reacquire_nobuf() can be used. 381 * However, on reacquire the buffer content is no longer available. A 382 * reacquire cannot be used to resume printing. 383 * 384 * The callback can be called from any context (including NMI). 385 * Therefore it must avoid usage of any locking and instead rely 386 * on the console ownership for synchronization. 387 */ 388 void (*write_atomic)(struct console *con, struct nbcon_write_context *wctxt); 389 390 /** 391 * @write_thread: 392 * 393 * NBCON callback to write out text in task context. 394 * 395 * This callback must be called only in task context with both 396 * device_lock() and the nbcon console acquired with 397 * NBCON_PRIO_NORMAL. 398 * 399 * The same rules for console ownership verification and unsafe 400 * sections handling applies as with write_atomic(). 401 * 402 * The console ownership handling is necessary for synchronization 403 * against write_atomic() which is synchronized only via the context. 404 * 405 * The device_lock() provides the primary serialization for operations 406 * on the device. It might be as relaxed (mutex)[*] or as tight 407 * (disabled preemption and interrupts) as needed. It allows 408 * the kthread to operate in the least restrictive mode[**]. 409 * 410 * [*] Standalone nbcon_context_try_acquire() is not safe with 411 * the preemption enabled, see nbcon_owner_matches(). But it 412 * can be safe when always called in the preemptive context 413 * under the device_lock(). 414 * 415 * [**] The device_lock() makes sure that nbcon_context_try_acquire() 416 * would never need to spin which is important especially with 417 * PREEMPT_RT. 418 */ 419 void (*write_thread)(struct console *con, struct nbcon_write_context *wctxt); 420 421 /** 422 * @device_lock: 423 * 424 * NBCON callback to begin synchronization with driver code. 425 * 426 * Console drivers typically must deal with access to the hardware 427 * via user input/output (such as an interactive login shell) and 428 * output of kernel messages via printk() calls. This callback is 429 * called by the printk-subsystem whenever it needs to synchronize 430 * with hardware access by the driver. It should be implemented to 431 * use whatever synchronization mechanism the driver is using for 432 * itself (for example, the port lock for uart serial consoles). 433 * 434 * The callback is always called from task context. It may use any 435 * synchronization method required by the driver. 436 * 437 * IMPORTANT: The callback MUST disable migration. The console driver 438 * may be using a synchronization mechanism that already takes 439 * care of this (such as spinlocks). Otherwise this function must 440 * explicitly call migrate_disable(). 441 * 442 * The flags argument is provided as a convenience to the driver. It 443 * will be passed again to device_unlock(). It can be ignored if the 444 * driver does not need it. 445 */ 446 void (*device_lock)(struct console *con, unsigned long *flags); 447 448 /** 449 * @device_unlock: 450 * 451 * NBCON callback to finish synchronization with driver code. 452 * 453 * It is the counterpart to device_lock(). 454 * 455 * This callback is always called from task context. It must 456 * appropriately re-enable migration (depending on how device_lock() 457 * disabled migration). 458 * 459 * The flags argument is the value of the same variable that was 460 * passed to device_lock(). 461 */ 462 void (*device_unlock)(struct console *con, unsigned long flags); 463 464 atomic_t __private nbcon_state; 465 atomic_long_t __private nbcon_seq; 466 struct nbcon_context __private nbcon_device_ctxt; 467 atomic_long_t __private nbcon_prev_seq; 468 469 struct printk_buffers *pbufs; 470 struct task_struct *kthread; 471 struct rcuwait rcuwait; 472 struct irq_work irq_work; 473 }; 474 475 #ifdef CONFIG_LOCKDEP 476 extern void lockdep_assert_console_list_lock_held(void); 477 #else 478 static inline void lockdep_assert_console_list_lock_held(void) 479 { 480 } 481 #endif 482 483 #ifdef CONFIG_DEBUG_LOCK_ALLOC 484 extern bool console_srcu_read_lock_is_held(void); 485 #else 486 static inline bool console_srcu_read_lock_is_held(void) 487 { 488 return 1; 489 } 490 #endif 491 492 extern int console_srcu_read_lock(void); 493 extern void console_srcu_read_unlock(int cookie); 494 495 extern void console_list_lock(void); 496 extern void console_list_unlock(void); 497 498 extern struct hlist_head console_list; 499 500 /** 501 * console_srcu_read_flags - Locklessly read flags of a possibly registered 502 * console 503 * @con: struct console pointer of console to read flags from 504 * 505 * Locklessly reading @con->flags provides a consistent read value because 506 * there is at most one CPU modifying @con->flags and that CPU is using only 507 * read-modify-write operations to do so. 508 * 509 * Requires console_srcu_read_lock to be held, which implies that @con might 510 * be a registered console. The purpose of holding console_srcu_read_lock is 511 * to guarantee that the console state is valid (CON_SUSPENDED/CON_ENABLED) 512 * and that no exit/cleanup routines will run if the console is currently 513 * undergoing unregistration. 514 * 515 * If the caller is holding the console_list_lock or it is _certain_ that 516 * @con is not and will not become registered, the caller may read 517 * @con->flags directly instead. 518 * 519 * Context: Any context. 520 * Return: The current value of the @con->flags field. 521 */ 522 static inline short console_srcu_read_flags(const struct console *con) 523 { 524 WARN_ON_ONCE(!console_srcu_read_lock_is_held()); 525 526 /* 527 * The READ_ONCE() matches the WRITE_ONCE() when @flags are modified 528 * for registered consoles with console_srcu_write_flags(). 529 */ 530 return data_race(READ_ONCE(con->flags)); 531 } 532 533 /** 534 * console_srcu_write_flags - Write flags for a registered console 535 * @con: struct console pointer of console to write flags to 536 * @flags: new flags value to write 537 * 538 * Only use this function to write flags for registered consoles. It 539 * requires holding the console_list_lock. 540 * 541 * Context: Any context. 542 */ 543 static inline void console_srcu_write_flags(struct console *con, short flags) 544 { 545 lockdep_assert_console_list_lock_held(); 546 547 /* This matches the READ_ONCE() in console_srcu_read_flags(). */ 548 WRITE_ONCE(con->flags, flags); 549 } 550 551 /* Variant of console_is_registered() when the console_list_lock is held. */ 552 static inline bool console_is_registered_locked(const struct console *con) 553 { 554 lockdep_assert_console_list_lock_held(); 555 return !hlist_unhashed(&con->node); 556 } 557 558 /* 559 * console_is_registered - Check if the console is registered 560 * @con: struct console pointer of console to check 561 * 562 * Context: Process context. May sleep while acquiring console list lock. 563 * Return: true if the console is in the console list, otherwise false. 564 * 565 * If false is returned for a console that was previously registered, it 566 * can be assumed that the console's unregistration is fully completed, 567 * including the exit() callback after console list removal. 568 */ 569 static inline bool console_is_registered(const struct console *con) 570 { 571 bool ret; 572 573 console_list_lock(); 574 ret = console_is_registered_locked(con); 575 console_list_unlock(); 576 return ret; 577 } 578 579 /** 580 * for_each_console_srcu() - Iterator over registered consoles 581 * @con: struct console pointer used as loop cursor 582 * 583 * Although SRCU guarantees the console list will be consistent, the 584 * struct console fields may be updated by other CPUs while iterating. 585 * 586 * Requires console_srcu_read_lock to be held. Can be invoked from 587 * any context. 588 */ 589 #define for_each_console_srcu(con) \ 590 hlist_for_each_entry_srcu(con, &console_list, node, \ 591 console_srcu_read_lock_is_held()) 592 593 /** 594 * for_each_console() - Iterator over registered consoles 595 * @con: struct console pointer used as loop cursor 596 * 597 * The console list and the &console.flags are immutable while iterating. 598 * 599 * Requires console_list_lock to be held. 600 */ 601 #define for_each_console(con) \ 602 lockdep_assert_console_list_lock_held(); \ 603 hlist_for_each_entry(con, &console_list, node) 604 605 #ifdef CONFIG_PRINTK 606 extern void nbcon_cpu_emergency_enter(void); 607 extern void nbcon_cpu_emergency_exit(void); 608 extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt); 609 extern void nbcon_write_context_set_buf(struct nbcon_write_context *wctxt, 610 char *buf, unsigned int len); 611 extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt); 612 extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt); 613 extern void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt); 614 extern bool nbcon_allow_unsafe_takeover(void); 615 extern bool nbcon_kdb_try_acquire(struct console *con, 616 struct nbcon_write_context *wctxt); 617 extern void nbcon_kdb_release(struct nbcon_write_context *wctxt); 618 619 /* 620 * Check if the given console is currently capable and allowed to print 621 * records. Note that this function does not consider the current context, 622 * which can also play a role in deciding if @con can be used to print 623 * records. 624 */ 625 static inline bool console_is_usable(struct console *con, short flags, bool use_atomic) 626 { 627 if (!(flags & CON_ENABLED)) 628 return false; 629 630 if ((flags & CON_SUSPENDED)) 631 return false; 632 633 if (flags & CON_NBCON) { 634 if (use_atomic) { 635 /* The write_atomic() callback is optional. */ 636 if (!con->write_atomic) 637 return false; 638 639 /* 640 * An unsafe write_atomic() callback is only usable 641 * when unsafe takeovers are allowed. 642 */ 643 if ((flags & CON_NBCON_ATOMIC_UNSAFE) && !nbcon_allow_unsafe_takeover()) 644 return false; 645 } 646 647 /* 648 * For the !use_atomic case, @printk_kthreads_running is not 649 * checked because the write_thread() callback is also used 650 * via the legacy loop when the printer threads are not 651 * available. 652 */ 653 } else { 654 if (!con->write) 655 return false; 656 } 657 658 /* 659 * Console drivers may assume that per-cpu resources have been 660 * allocated. So unless they're explicitly marked as being able to 661 * cope (CON_ANYTIME) don't call them until this CPU is officially up. 662 */ 663 if (!cpu_online(raw_smp_processor_id()) && !(flags & CON_ANYTIME)) 664 return false; 665 666 return true; 667 } 668 669 #else 670 static inline void nbcon_cpu_emergency_enter(void) { } 671 static inline void nbcon_cpu_emergency_exit(void) { } 672 static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; } 673 static inline void nbcon_write_context_set_buf(struct nbcon_write_context *wctxt, 674 char *buf, unsigned int len) { } 675 static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; } 676 static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; } 677 static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) { } 678 static inline bool nbcon_kdb_try_acquire(struct console *con, 679 struct nbcon_write_context *wctxt) { return false; } 680 static inline void nbcon_kdb_release(struct nbcon_write_context *wctxt) { } 681 static inline bool console_is_usable(struct console *con, short flags, 682 bool use_atomic) { return false; } 683 #endif 684 685 extern int console_set_on_cmdline; 686 extern struct console *early_console; 687 688 enum con_flush_mode { 689 CONSOLE_FLUSH_PENDING, 690 CONSOLE_REPLAY_ALL, 691 }; 692 693 extern int add_preferred_console(const char *name, const short idx, char *options); 694 extern void console_force_preferred_locked(struct console *con); 695 extern void register_console(struct console *); 696 extern int unregister_console(struct console *); 697 extern void console_lock(void); 698 extern int console_trylock(void); 699 extern void console_unlock(void); 700 extern void console_unblank(void); 701 extern void console_flush_on_panic(enum con_flush_mode mode); 702 extern struct tty_driver *console_device(int *); 703 extern void console_suspend(struct console *); 704 extern void console_resume(struct console *); 705 extern int is_console_locked(void); 706 extern int braille_register_console(struct console *, int index, 707 char *console_options, char *braille_options); 708 extern int braille_unregister_console(struct console *); 709 #ifdef CONFIG_TTY 710 extern void console_sysfs_notify(void); 711 #else 712 static inline void console_sysfs_notify(void) 713 { } 714 #endif 715 extern bool console_suspend_enabled; 716 717 /* Suspend and resume console messages over PM events */ 718 extern void console_suspend_all(void); 719 extern void console_resume_all(void); 720 721 int mda_console_init(void); 722 723 void vcs_make_sysfs(int index); 724 void vcs_remove_sysfs(int index); 725 726 /* Some debug stub to catch some of the obvious races in the VT code */ 727 #define WARN_CONSOLE_UNLOCKED() \ 728 WARN_ON(!atomic_read(&ignore_console_lock_warning) && \ 729 !is_console_locked() && !oops_in_progress) 730 /* 731 * Increment ignore_console_lock_warning if you need to quiet 732 * WARN_CONSOLE_UNLOCKED() for debugging purposes. 733 */ 734 extern atomic_t ignore_console_lock_warning; 735 736 DEFINE_LOCK_GUARD_0(console_lock, console_lock(), console_unlock()); 737 738 extern void console_init(void); 739 740 /* For deferred console takeover */ 741 void dummycon_register_output_notifier(struct notifier_block *nb); 742 void dummycon_unregister_output_notifier(struct notifier_block *nb); 743 744 #endif /* _LINUX_CONSOLE_H */ 745