第8章、linux设备驱动中的阻塞与非io

1、 !#$%&()*+,-. !#$%&()*+,-.第 8 章Linux 设备驱动中的阻塞与非阻塞 I/O阻塞和非阻塞 I/O 是设备的两种不同模式，驱动程序可以灵活地支持用户空间对设备的这两种方式。节讲解阻塞 I/O 和非阻塞 I/O 的区别，实现阻塞 I/O 的等待队列机制，以及在globalfifo 设备驱动中增加对阻塞 I/O 支持的方法，并进行了用户空间的验证。节讲解设备驱动的轮询（poll）操作的概念和编程方法，poll 操作可以帮助用户了解是否能对设备进行无阻塞。8.3 节讲解在 globalfifo 中增加 poll 操作的方法，并进行了用户空间的验证。=wxB!io01wx#

2、$G%&()*+nKJ,-./Mwx0123nowx4*+nKn!5678J49:;?J,-bcwxnGno01wx#mG*+JABCDEJBCGFQGtJ,HMNnowxIJ23KLKLMNOPYQR.STTKLno read()Uwrite()bVW:T#J$01Z01J23KLTi0123,-(MN%XJ2JTTKL read()Uwrite()b:T_JabcKdenopfgZ01m1J)S01(GM%X#J01239rstu+vwxyz|J)GeJ 0123G=J)TU!%X01(GFQGtJY#$ %Q& CPU (=G%X(nK$n!5678J,J-.g/i0bQZ12356n

3、K23nKQZ45M56i;78sJ,I91(%&H#:;q0b;7=8.1 AA=ZCD0brE=FIJHMIJKusigactionvNLMZCDNON CPU OTJY8PPBIpQR=?=?= I/O8.1.1bcdei Linux 23KL;JMNGTbcdeuwait queuevva=nK23wait queue STUxI0bVWXZai Linux 8pJANdeIV_aJ?nK:;fgbcdJ1Tea;LMf1KkfgbcdeMNTvHMXVW(cdevaJ9 7 :;ghJKii;pjkbLinux 2.6 OP+lebcdewx10123456789:20;=34567

4、89:+s DECLARE_WAIT_QUEUE_HEAD()mMNxInompqrbcdestuvZw30124567:xmTenompqr0byI name ?/A4567:add_wait_queue()Tebcde wait zk-bcdes q !bcde|;J remove_wait_queue()Tebcde wait 9bcdes q ! 5045BC:bc90b! queue xIbcdeswait_event()A wait_event_erruptible()_ie2 CMN4JK$7J%CGkt_timeout 2bc/*789:;?ABCDE*/ while(0)#d

5、efinedo wait_event(wq,condition)DEFINE_WAIT( wait); ERRUPTIBLE);for (;) prepare_to_wait(&wq, if (condition)break;& wait,TASK_UNschedule();/*FG CPU*/finish_wait(&wq, & wait); while (0)void fastcall22 prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait,se)232425262728293031323334unsigned long fla

6、gs;wait-flags &= WQ_FLAG_EXCLUSIVE; spin_lock_irqsave(&q-lock, flags); if (list_empty(&wait-task_list) add_wait_queue(q, wait);/=?ABif (is_sync_wait(wait)set_current_se(se);/HI JKLMNOPQRspin_unlock_irqrestore(&q-lock, flags);35 void fastcall finish_wait(wait_queue_head_t *q, wait_queue_t *wait) 36 3

7、7 unsigned long flags;60FG67:thwx$23N queue xIbcdesgibcde;giexbcdesbcdeXTnKwake_up() T ? wait_event() Bwait_event_timeout() , X G TJ Bewake_up_erruptible()T, X?Gwait_event_erruptible() wake_up() M 2 3wait_event_erruptible_timeout()T-JTASK_ERRUPTIBLEATASK_UNERRUPTIBLE n Kwake_up_erruptible()23-e TASK

8、_ERRUPTIBLE nK70H4567IJK:sleep_on().xTUB/%nK780, TASK_UNERRUPTIBLEJmno0bbcdeJ122A-bcdes qJ,-(M%&Jq 34b cde423erruptible_sleep_on()? sleep_on().5wJ*xTB/%nK780,TASK_ERRUPTIBLEJmno0bbcdeJ122A-bcdes qJ,-(M%&Jq 34bcde423BCnK6-JKsleep_on() . T x ? wake_up() , X G TJerruptible_sleep_on() T x ?wake_up_errup

9、tible(),XGT=8.4 A=(task_list) spin_lock_irqsave(&q-lock, flags);list_del_init(&wait-task_list);spin_unlock_irqrestore(&q-lock, flags); 44 45 8.4sleep_on()DE ! !8.5erruptible_sleep_on()DE9 = 8.4 A Zbcdesi;GTset_current_se().B_ _add_wait_queue().va/%nK789:J,;se = TASK_UNERRUPTIBLE 5w?pBMoKLAJset_curre

10、nt_se().iBCDE+8MNGTJG$Fim 5DGJHBN|e_ _add_ wait_queue(),JiIJ0123;JmG:T sleep_on()Berruptible_sleep_on()JBKLnonK789:AMNJse = TASK_ERRUPTIBLE;/HI JKLNO 6SLEEP_ON_HEADschedule();/FG CPUSLEEP_ON_TAIL10 1 void fastcall _ _schederruptible_sleep_on(wait_queue_head_t *q) 2 SLEEP_ON_VAR/* #define SLEEP_ON_VA

11、Runsigned long flags;wait_queue_t wait;init_waitqueue_entry(&wait, current); */current-se = TASK_UNERRUPTIBLE;/HI JKLNO 9SLEEP_ON_HEAD/* #define SLEEP_ON_HEADspin_lock_irqsave(&q-lock,flags);_ _add_wait_queue(q, &wait);spin_unlock(&q-lock);*/ 15schedule();/FG CPUSLEEP_ON_TAIL/* #define SLEEP_ON_TAIL

12、spin_lock_irq(&q-lock);_ _remove_wait_queue(q, &wait);spin_unlock_irqrestore(&q-lock, flags); */ 22 !8.6 HLMNOPQRSNTUVWX schedule()ic ssize_t_write(struct file *file, const char *buffer,1 ssize_t234567891011121314151617181920212223242526272829303132333435363738count, loff_t *p.)DECLARE_WAITQUEUE(wai

13、t, current); /UV?AB_ _add_wait_queue(&_wait, &wait); /=?ABret = count;/* ?WXYZ */ doavail = device_writable(.); if (avail 0)_ _set_current_se(TASK_ERRUPTIBLE);/HIKLNOif (avail f_flags &O_NONBLOCK) /DEif (!ret)ret = - EAGAIN;goto out;schedule(); /_abKLcdif (signal_pending(current)/efghPijklif (!ret)r

14、et = - ERESTARTSYS;goto out;while (avail wx globalfifo 0123) globalfifo jkYQQR.2 globalfifo ;STF:,0b FIFOJiS FIFO ;i_#UuoinK2_V-Yb FIFO hi4BnKB VvJBnK2_BZJ2_$9 globalfifo STF;4WXl iS FIFO .#uoHi0YVWZ4VJBV.24BnK9Yb FIFO ;BZp_vJVnK:Yb FIFO ;V!_aiJ globalfifo yItglobalfifowJi globalfifo ;JB FIFO 23V FI

15、FOJV FIFO p23B FIFOJMN_901aJi*;jkEbbcdeAVJ=8.7 gAsJ?_XT !8.7 globalfifo YZ? globalfifo01aa0bGHBjkp current_len ,bTec/%FIFO ;i_d;YbbcdeMi0123Iekf.;:T init_waitqueue_head()4pqrJg0123Iekf.w_wait423r_waitJprivate_data; /+,WXrs t-.DECLARE_WAITQUEUE(wait, current); /124567813 if (ret sem); /*()ij!*/init_w

16、aitqueue_head(&globalfifo_devp-r_wait); /*;w_wait); /*;sem); /+,ij!add_wait_queue(&dev-r_wait, &wait); /Se45678/* ? FIFO / */(dev-current_len = 0)ifif (filp-f_flags &O_NONBLOCK)ret = - EAGAIN;goto out;_ _set_current_se(TASK_ERRUPTIBLE);/HIKLNOP0R21222324252627282930313233343536373839404142434445up(&

17、dev-sem);schedule(); /_abKLcd if (signal_pending(current)/efghPijklret = - ERESTARTSYS;goto out2;down(&dev-sem);/*if1 2/3 */(count dev-current_len)count = dev-current_len;(copy_to_user(buf, dev-mem,ifcount)ret = - EFAULT;goto out;elsememcpy(dev-mem, dev-mem + count, dev-current_len - count);/fifo vw

18、Jn46dev-current_len -= count; /$uvwx45prk(KERN_INFO read %d bytes(s),current_len:%dn, count,47dev-current_len);48495051525354558A56575859606162wake_up_erruptible(&dev-w_wait); /FG_4567ret = count;out: up(&dev-sem); /ij!out2: remove_wait_queue(&dev-w_wait, &wait); /fgh4567set_current_s return ret;e(T

19、ASK_RUNNING);/*globalfifo 78*/ic ssize_t globalfifo_write(struct file *filp, const char_s_user *buf,size_tcount, loff_t *p636465t-.66676869707172737475767778798081K8283848586878889909192939495)globalfifo_dev *dev = filp-private_data; /+,WXrsstructret;DECLARE_WAITQUEUE(wait, current); /124567down(&de

20、v-sem); /+6ij!add_wait_queue(&dev-w_wait, &wait); /Se_45678/* ? FIFO 9 */(dev-current_len = GLOBALFIFO_SIZE)ifif (filp-f_flags &O_NONBLOCK)/efgDEret = - EAGAIN;goto out;_ _set_current_se(TASK_ERRUPTIBLE);/QRSNTUiJup(&dev-sem);schedule(); /WjklSNmn if (signal pending(current)/opqristFGret = - ERESTAR

21、TSYS;goto out2;down(&dev-sem); /+,ij!/*; 2/31/3*/=8.9 -hpbcdenZAnKMNcurrent_len != 0 r_wait,dev-current_len != 0 vkNJ 2V. ; 05 i Tebc dev-current_len !=GLOBALFIFO_SIZE w_wait,dev-current_len != 0vkNlmFt JU ng bc de V A . r_wait, dev- current_len != 0 v A9 13 p 32 o=w_wait, dev- current_len != 0vA9 7

22、3p93 o=XqS0Qrs_ai9 13p32 o=A9 73p93 osemvJ)uvGMwxy 8.1uavgAJz0/%current_len I 0J# i 0 b B nKJ A $ %& JKi J , I01 G ./ J A , I wait_event_ erruptible(dev-r_wait, dev- current_len != 0) =J dev-r_wait bcdeh( dev-current_len != 0 wxYMNiVnK;noJVnpJKiY0rs3xyoJoVwx%Y-.bcBnKsJ9uvJKiJ,|bcXZ(Ty 8.1ubvgAJz0/%c

23、urrent_len IGLOBALFIFO_SIZEJ # i 0 b V nKJ A % & J K i J , I01 G ./ J A , Iwait_event_erruptiblue dev-w_wait, dev-current_len != GLOBALFIFO_SIZEv=Jif (count GLOBALFIFO_SIZE - dev-current_len)count = GLOBALFIFO_SIZE - dev-current_len; 9899if (copy_from_user(dev-mem + dev-current_len, buf, count)100re

24、t = - EFAULT;goto out;103104else105dev-current_len += count;prk(KERN_INFO written %d bytes(s),current_len:%dn, count, dev-current_len);wake_up_erruptible(&dev-r_wait); /FG4567ret = count;113114out: up(&dev-sem); /ij!out2: remove_wait_queue(&dev-w_wait, &wait); /;=M?AB pn?set_current_se(TASK_RUNNING)

25、;return ret;119 而dev-w_wait 等待队列及让dev-current_ len != GLOBALFIFO_SIZE 的操作又需要在读进程中进行，读进执行读操作前又必须等待写进程信号量，造成互相等待对方资源的局面，从而死锁。所谓死锁，就是多个进程循环等待它方占有的资源而无限期地僵持下去的局面。如果没有外力的作用，那么死锁涉及的各个进程都将处于状态。因此，驱动工程师一定要注意：当多个等待队列、信号量等机制同时出现时，谨防死锁。现在回过来看一下代码8.9 的第 15 行和第 75 行，发现在设备驱动的 read()、write()等功能函数中，可以通过 filp-f_flag

26、s 标志获得用户空间是否要求非阻塞。驱动中可以依据此标志判断用户究竟要求阻塞还是非阻塞理。，从而进行不同的处S echo nK/dev/globalfifo V!0C_Jcat nKUnoxC_?aZv8.2.1st?=l I/O select()A poll()VW:T4A$0123; poll().4oJi 2.5.45 ;H3!p epoll()JoBC poll()select()A poll()VW:TWD0QJ%Ci BSD UNIX ;3!J2Ci System V;3!stwxrootlocalhost root# a great ChiLinux driver Enginee

27、r8.2.2TTKL;stKTTKL;4EFT-B BSD UNIX ;3! select()VW:TJ*GH+.*; readfdsUwritefdsUexceptfds ?_B4 select()IJBUVALL-hm 1KhELdJnumfds BMNMGK=4Nm1KhEk 1timeout !B0b! struct timeval 5H!NJAMNG select()ibc timeout #W2$him1KhEO1P)_struct timeval _ano=8.10 gA !8.10 timeval 12+ewxTv00U U57m1KhELd 0bm1KhEL0bm1KhEk!

28、m1KhEL;0bm1KhE9m1KhEL; 57m1KhEB40Y8.2.30123;stK0123; poll().GH+.90b!I file a!NJ9#b!Ist!NYb.TxnoN+EQ-xXM3+01m178:rbcde:T poll_wait().JXTBUVR=lSTe poll_tablebcde poll_wait().GH+.poll_wait().QbcZf1poll_wait().g- xB2S%nKzk- wait !nbceupoll_tablev;23KL poll().Tx_01(M%X78Jo POLLINUPOLLOUTUPOLLPRIUPOLLERRU

29、POLLNVAL bmbmo8R01void poll_wait(struct file *filp, wait_queue_heat_t *queue, poll_table* wait);unsigned(*poll)(struct file * filp, struct poll_table* wait);FD_ISSET(fd,fd_set *set)FD_CLR(fd,fd_set *set)FD_SET(fd,fd_set *set)FD_ZERO(fd_set *set)struct timevaltv_sec; /* */ tv_usec; /* AB */;select(nu

30、mfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,struct timeval *timeout);QBJPOLLOUTunoI 0 x0004vyz01MN =QVKcNt?JZ0123; poll().HI_J=8.11 gA !8.11poll()DEuvw8.3.1i globalfifo 23;jkstwxi globalfifo poll().;J01a;current_len Bbe 0 v%&01current_len Bbe GLOBALFIFO_SIZE v%&01MV78J=8.12 gA !8.12 g

31、lobalfifo YZLM poll()DE1 sic unsignedglobalfifo_poll(struct file *filp, poll_table*wait)2 3unsignedmask = 0;RSstwxprivate_data; /*+,WXrst-.*/ 56.poll_wait(filp, &dev-r_wait, wait);/5?ABppoll_wait(filp, &dev-w_wait, wait);/?ABp 910if (.)/51112mask |= POLLIN | POLLRDNORM; /*CDvw+,*/ 131415if (.)/1617m

32、ask |= POLLOUT | POLLWRNORM; /*CDvw&*/ 181920.21return mask; 22 /yN2 globalfifo_poll =) globalfifo_fops poll ,bJ+gA.8.3.2iTUVWqr globalfifo 01stV0bTTKL pollmonitor.c Te8.13 gAglobalfifo MBV78JYbKLprivate_data; /*+,WXrs t-.*/56down(&dev-sem); 7poll_wait(filp, &dev-r_wait, wait);poll_wait(filp, &dev-w

33、_wait, wait);10/*fifo /*/11if (dev-current_len != 0) 1213mask |= POLLIN | POLLRDNORM; /*CDvw+,*/ 1415/*fifo 9*/16if (dev-current_len != GLOBALFIFO_SIZE) 1718mask |= POLLOUT | POLLWRNORM; /*CDvw&*/ 1920up(&dev-sem);return mask; 23 =o#+-JShiBC!Jo FIFO IV#JKLG7QZtPoll monitor:canbe writtenwlSKc echo /dev/globalfifo V!0Y_2JZtPoll monitor:can be readwAtPoll monitor:can be writtenwl G7QKc echo /dev/globalfifo Vchar rd_chB