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Annotation of linux/fs/select.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * This file contains the procedures for the handling of select
        !             3:  *
        !             4:  * Created for Linux based loosely upon Mathius Lattner's minix
        !             5:  * patches by Peter MacDonald. Heavily edited by Linus.
        !             6:  */
        !             7: 
        !             8: #include <linux/fs.h>
        !             9: #include <linux/kernel.h>
        !            10: #include <linux/tty.h>
        !            11: #include <linux/sched.h>
        !            12: 
        !            13: #include <asm/segment.h>
        !            14: #include <asm/system.h>
        !            15: 
        !            16: #include <sys/stat.h>
        !            17: #include <sys/types.h>
        !            18: #include <string.h>
        !            19: #include <const.h>
        !            20: #include <errno.h>
        !            21: #include <sys/time.h>
        !            22: #include <signal.h>
        !            23: 
        !            24: /*
        !            25:  * Ok, Peter made a complicated, but straightforward multiple_wait() function.
        !            26:  * I have rewritten this, taking some shortcuts: This code may not be easy to
        !            27:  * follow, but it should be free of race-conditions, and it's practical. If you
        !            28:  * understand what I'm doing here, then you understand how the linux sleep/wakeup
        !            29:  * mechanism works.
        !            30:  *
        !            31:  * Two very simple procedures, add_wait() and free_wait() make all the work. We
        !            32:  * have to have interrupts disabled throughout the select, but that's not really
        !            33:  * such a loss: sleeping automatically frees interrupts when we aren't in this
        !            34:  * task.
        !            35:  */
        !            36: 
        !            37: typedef struct {
        !            38:        struct task_struct * old_task;
        !            39:        struct task_struct ** wait_address;
        !            40: } wait_entry;
        !            41: 
        !            42: typedef struct {
        !            43:        int nr;
        !            44:        wait_entry entry[NR_OPEN*3];
        !            45: } select_table;
        !            46: 
        !            47: static void add_wait(struct task_struct ** wait_address, select_table * p)
        !            48: {
        !            49:        int i;
        !            50: 
        !            51:        if (!wait_address)
        !            52:                return;
        !            53:        for (i = 0 ; i < p->nr ; i++)
        !            54:                if (p->entry[i].wait_address == wait_address)
        !            55:                        return;
        !            56:        p->entry[p->nr].wait_address = wait_address;
        !            57:        p->entry[p->nr].old_task = * wait_address;
        !            58:        *wait_address = current;
        !            59:        p->nr++;
        !            60: }
        !            61: 
        !            62: static void free_wait(select_table * p)
        !            63: {
        !            64:        int i;
        !            65:        struct task_struct ** tpp;
        !            66: 
        !            67:        for (i = 0; i < p->nr ; i++) {
        !            68:                tpp = p->entry[i].wait_address;
        !            69:                while (*tpp && *tpp != current) {
        !            70:                        (*tpp)->state = 0;
        !            71:                        current->state = TASK_UNINTERRUPTIBLE;
        !            72:                        schedule();
        !            73:                }
        !            74:                if (!*tpp)
        !            75:                        printk("free_wait: NULL");
        !            76:                if (*tpp = p->entry[i].old_task)
        !            77:                        (**tpp).state = 0;
        !            78:        }
        !            79:        p->nr = 0;
        !            80: }
        !            81: 
        !            82: static struct tty_struct * get_tty(struct m_inode * inode)
        !            83: {
        !            84:        int major, minor;
        !            85: 
        !            86:        if (!S_ISCHR(inode->i_mode))
        !            87:                return NULL;
        !            88:        if ((major = MAJOR(inode->i_zone[0])) != 5 && major != 4)
        !            89:                return NULL;
        !            90:        if (major == 5)
        !            91:                minor = current->tty;
        !            92:        else
        !            93:                minor = MINOR(inode->i_zone[0]);
        !            94:        if (minor < 0)
        !            95:                return NULL;
        !            96:        return TTY_TABLE(minor);
        !            97: }
        !            98: 
        !            99: /*
        !           100:  * The check_XX functions check out a file. We know it's either
        !           101:  * a pipe, a character device or a fifo (fifo's not implemented)
        !           102:  */
        !           103: static int check_in(select_table * wait, struct m_inode * inode)
        !           104: {
        !           105:        struct tty_struct * tty;
        !           106: 
        !           107:        if (tty = get_tty(inode))
        !           108:                if (!EMPTY(tty->secondary))
        !           109:                        return 1;
        !           110:                else
        !           111:                        add_wait(&tty->secondary->proc_list, wait);
        !           112:        else if (inode->i_pipe)
        !           113:                if (!PIPE_EMPTY(*inode))
        !           114:                        return 1;
        !           115:                else
        !           116:                        add_wait(&inode->i_wait, wait);
        !           117:        return 0;
        !           118: }
        !           119: 
        !           120: static int check_out(select_table * wait, struct m_inode * inode)
        !           121: {
        !           122:        struct tty_struct * tty;
        !           123: 
        !           124:        if (tty = get_tty(inode))
        !           125:                if (!FULL(tty->write_q))
        !           126:                        return 1;
        !           127:                else
        !           128:                        add_wait(&tty->write_q->proc_list, wait);
        !           129:        else if (inode->i_pipe)
        !           130:                if (!PIPE_FULL(*inode))
        !           131:                        return 1;
        !           132:                else
        !           133:                        add_wait(&inode->i_wait, wait);
        !           134:        return 0;
        !           135: }
        !           136: 
        !           137: static int check_ex(select_table * wait, struct m_inode * inode)
        !           138: {
        !           139:        struct tty_struct * tty;
        !           140: 
        !           141:        if (tty = get_tty(inode))
        !           142:                if (!FULL(tty->write_q))
        !           143:                        return 0;
        !           144:                else
        !           145:                        return 0;
        !           146:        else if (inode->i_pipe)
        !           147:                if (inode->i_count < 2)
        !           148:                        return 1;
        !           149:                else
        !           150:                        add_wait(&inode->i_wait,wait);
        !           151:        return 0;
        !           152: }
        !           153: 
        !           154: int do_select(fd_set in, fd_set out, fd_set ex,
        !           155:        fd_set *inp, fd_set *outp, fd_set *exp)
        !           156: {
        !           157:        int count;
        !           158:        select_table wait_table;
        !           159:        int i;
        !           160:        fd_set mask;
        !           161: 
        !           162:        mask = in | out | ex;
        !           163:        for (i = 0 ; i < NR_OPEN ; i++,mask >>= 1) {
        !           164:                if (!(mask & 1))
        !           165:                        continue;
        !           166:                if (!current->filp[i])
        !           167:                        return -EBADF;
        !           168:                if (!current->filp[i]->f_inode)
        !           169:                        return -EBADF;
        !           170:                if (current->filp[i]->f_inode->i_pipe)
        !           171:                        continue;
        !           172:                if (S_ISCHR(current->filp[i]->f_inode->i_mode))
        !           173:                        continue;
        !           174:                if (S_ISFIFO(current->filp[i]->f_inode->i_mode))
        !           175:                        continue;
        !           176:                return -EBADF;
        !           177:        }
        !           178: repeat:
        !           179:        wait_table.nr = 0;
        !           180:        *inp = *outp = *exp = 0;
        !           181:        count = 0;
        !           182:        mask = 1;
        !           183:        for (i = 0 ; i < NR_OPEN ; i++, mask += mask) {
        !           184:                if (mask & in)
        !           185:                        if (check_in(&wait_table,current->filp[i]->f_inode)) {
        !           186:                                *inp |= mask;
        !           187:                                count++;
        !           188:                        }
        !           189:                if (mask & out)
        !           190:                        if (check_out(&wait_table,current->filp[i]->f_inode)) {
        !           191:                                *outp |= mask;
        !           192:                                count++;
        !           193:                        }
        !           194:                if (mask & ex)
        !           195:                        if (check_ex(&wait_table,current->filp[i]->f_inode)) {
        !           196:                                *exp |= mask;
        !           197:                                count++;
        !           198:                        }
        !           199:        }
        !           200:        if (!(current->signal & ~current->blocked) &&
        !           201:            (wait_table.nr || current->timeout) && !count) {
        !           202:                current->state = TASK_INTERRUPTIBLE;
        !           203:                schedule();
        !           204:                free_wait(&wait_table);
        !           205:                goto repeat;
        !           206:        }
        !           207:        free_wait(&wait_table);
        !           208:        return count;
        !           209: }
        !           210: 
        !           211: /*
        !           212:  * Note that we cannot return -ERESTARTSYS, as we change our input
        !           213:  * parameters. Sad, but there you are. We could do some tweaking in
        !           214:  * the library function ...
        !           215:  */
        !           216: int sys_select( unsigned long *buffer )
        !           217: {
        !           218: /* Perform the select(nd, in, out, ex, tv) system call. */
        !           219:        int i;
        !           220:        fd_set res_in, in = 0, *inp;
        !           221:        fd_set res_out, out = 0, *outp;
        !           222:        fd_set res_ex, ex = 0, *exp;
        !           223:        fd_set mask;
        !           224:        struct timeval *tvp;
        !           225:        unsigned long timeout;
        !           226: 
        !           227:        mask = ~((~0) << get_fs_long(buffer++));
        !           228:        inp = (fd_set *) get_fs_long(buffer++);
        !           229:        outp = (fd_set *) get_fs_long(buffer++);
        !           230:        exp = (fd_set *) get_fs_long(buffer++);
        !           231:        tvp = (struct timeval *) get_fs_long(buffer);
        !           232: 
        !           233:        if (inp)
        !           234:                in = mask & get_fs_long(inp);
        !           235:        if (outp)
        !           236:                out = mask & get_fs_long(outp);
        !           237:        if (exp)
        !           238:                ex = mask & get_fs_long(exp);
        !           239:        timeout = 0xffffffff;
        !           240:        if (tvp) {
        !           241:                timeout = get_fs_long((unsigned long *)&tvp->tv_usec)/(1000000/HZ);
        !           242:                timeout += get_fs_long((unsigned long *)&tvp->tv_sec) * HZ;
        !           243:                timeout += jiffies;
        !           244:        }
        !           245:        current->timeout = timeout;
        !           246:        cli();
        !           247:        i = do_select(in, out, ex, &res_in, &res_out, &res_ex);
        !           248:        if (current->timeout > jiffies)
        !           249:                timeout = current->timeout - jiffies;
        !           250:        else
        !           251:                timeout = 0;
        !           252:        sti();
        !           253:        current->timeout = 0;
        !           254:        if (i < 0)
        !           255:                return i;
        !           256:        if (inp) {
        !           257:                verify_area(inp, 4);
        !           258:                put_fs_long(res_in,inp);
        !           259:        }
        !           260:        if (outp) {
        !           261:                verify_area(outp,4);
        !           262:                put_fs_long(res_out,outp);
        !           263:        }
        !           264:        if (exp) {
        !           265:                verify_area(exp,4);
        !           266:                put_fs_long(res_ex,exp);
        !           267:        }
        !           268:        if (tvp) {
        !           269:                verify_area(tvp, sizeof(*tvp));
        !           270:                put_fs_long(timeout/HZ, (unsigned long *) &tvp->tv_sec);
        !           271:                timeout %= HZ;
        !           272:                timeout *= (1000000/HZ);
        !           273:                put_fs_long(timeout, (unsigned long *) &tvp->tv_usec);
        !           274:        }
        !           275:        if (!i && (current->signal & ~current->blocked))
        !           276:                return -EINTR;
        !           277:        return i;
        !           278: }

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