306 lines
10 KiB
C
306 lines
10 KiB
C
/* This file deals with the suspension and revival of processes. A process can
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* be suspended because it wants to read or write from a pipe and can't, or
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* because it wants to read or write from a special file and can't. When a
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* process can't continue it is suspended, and revived later when it is able
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* to continue.
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*
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* The entry points into this file are
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* do_pipe: perform the PIPE system call
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* pipe_check: check to see that a read or write on a pipe is feasible now
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* suspend: suspend a process that cannot do a requested read or write
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* release: check to see if a suspended process can be released and do it
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* revive: mark a suspended process as able to run again
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* do_unpause: a signal has been sent to a process; see if it suspended
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*/
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#include "fs.h"
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#include <fcntl.h>
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#include <signal.h>
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#include <minix/callnr.h>
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#include <minix/com.h>
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#include "dmap.h"
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#include "file.h"
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#include "fproc.h"
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#include "inode.h"
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#include "param.h"
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#include "super.h"
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/*===========================================================================*
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* do_pipe *
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*===========================================================================*/
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PUBLIC int do_pipe()
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{
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/* Perform the pipe(fil_des) system call. */
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register struct fproc *rfp;
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register struct inode *rip;
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int r;
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struct filp *fil_ptr0, *fil_ptr1;
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int fil_des[2]; /* reply goes here */
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/* Acquire two file descriptors. */
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rfp = fp;
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if ( (r = get_fd(0, R_BIT, &fil_des[0], &fil_ptr0)) != OK) return(r);
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rfp->fp_filp[fil_des[0]] = fil_ptr0;
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fil_ptr0->filp_count = 1;
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if ( (r = get_fd(0, W_BIT, &fil_des[1], &fil_ptr1)) != OK) {
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rfp->fp_filp[fil_des[0]] = NIL_FILP;
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fil_ptr0->filp_count = 0;
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return(r);
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}
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rfp->fp_filp[fil_des[1]] = fil_ptr1;
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fil_ptr1->filp_count = 1;
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/* Make the inode on the pipe device. */
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if ( (rip = alloc_inode(root_dev, I_REGULAR) ) == NIL_INODE) {
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rfp->fp_filp[fil_des[0]] = NIL_FILP;
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fil_ptr0->filp_count = 0;
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rfp->fp_filp[fil_des[1]] = NIL_FILP;
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fil_ptr1->filp_count = 0;
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return(err_code);
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}
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if (read_only(rip) != OK) panic("pipe device is read only", NO_NUM);
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rip->i_pipe = I_PIPE;
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rip->i_mode &= ~I_REGULAR;
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rip->i_mode |= I_NAMED_PIPE; /* pipes and FIFOs have this bit set */
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fil_ptr0->filp_ino = rip;
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fil_ptr0->filp_flags = O_RDONLY;
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dup_inode(rip); /* for double usage */
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fil_ptr1->filp_ino = rip;
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fil_ptr1->filp_flags = O_WRONLY;
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rw_inode(rip, WRITING); /* mark inode as allocated */
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m_out.reply_i1 = fil_des[0];
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m_out.reply_i2 = fil_des[1];
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rip->i_update = ATIME | CTIME | MTIME;
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return(OK);
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}
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/*===========================================================================*
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* pipe_check *
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*===========================================================================*/
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PUBLIC int pipe_check(rip, rw_flag, oflags, bytes, position, canwrite)
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register struct inode *rip; /* the inode of the pipe */
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int rw_flag; /* READING or WRITING */
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int oflags; /* flags set by open or fcntl */
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register int bytes; /* bytes to be read or written (all chunks) */
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register off_t position; /* current file position */
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int *canwrite; /* return: number of bytes we can write */
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{
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/* Pipes are a little different. If a process reads from an empty pipe for
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* which a writer still exists, suspend the reader. If the pipe is empty
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* and there is no writer, return 0 bytes. If a process is writing to a
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* pipe and no one is reading from it, give a broken pipe error.
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*/
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/* If reading, check for empty pipe. */
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if (rw_flag == READING) {
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if (position >= rip->i_size) {
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/* Process is reading from an empty pipe. */
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int r = 0;
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if (find_filp(rip, W_BIT) != NIL_FILP) {
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/* Writer exists */
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if (oflags & O_NONBLOCK) {
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r = EAGAIN;
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} else {
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suspend(XPIPE); /* block reader */
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r = SUSPEND;
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}
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/* If need be, activate sleeping writers. */
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if (susp_count > 0) release(rip, WRITE, susp_count);
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}
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return(r);
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}
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} else {
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/* Process is writing to a pipe. */
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if (find_filp(rip, R_BIT) == NIL_FILP) {
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/* Tell kernel to generate a SIGPIPE signal. */
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sys_kill((int)(fp - fproc), SIGPIPE);
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return(EPIPE);
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}
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if (position + bytes > PIPE_SIZE(rip->i_sp->s_block_size)) {
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if ((oflags & O_NONBLOCK) && bytes < PIPE_SIZE(rip->i_sp->s_block_size))
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return(EAGAIN);
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else if ((oflags & O_NONBLOCK) && bytes > PIPE_SIZE(rip->i_sp->s_block_size)) {
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if ( (*canwrite = (PIPE_SIZE(rip->i_sp->s_block_size) - position)) > 0) {
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/* Do a partial write. Need to wakeup reader */
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release(rip, READ, susp_count);
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return(1);
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} else {
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return(EAGAIN);
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}
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}
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if (bytes > PIPE_SIZE(rip->i_sp->s_block_size)) {
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if ((*canwrite = PIPE_SIZE(rip->i_sp->s_block_size) - position) > 0) {
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/* Do a partial write. Need to wakeup reader
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* since we'll suspend ourself in read_write()
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*/
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release(rip, READ, susp_count);
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return(1);
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}
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}
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suspend(XPIPE); /* stop writer -- pipe full */
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return(SUSPEND);
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}
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/* Writing to an empty pipe. Search for suspended reader. */
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if (position == 0) release(rip, READ, susp_count);
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}
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*canwrite = 0;
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return(1);
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}
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/*===========================================================================*
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* suspend *
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*===========================================================================*/
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PUBLIC void suspend(task)
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int task; /* who is proc waiting for? (PIPE = pipe) */
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{
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/* Take measures to suspend the processing of the present system call.
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* Store the parameters to be used upon resuming in the process table.
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* (Actually they are not used when a process is waiting for an I/O device,
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* but they are needed for pipes, and it is not worth making the distinction.)
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* The SUSPEND pseudo error should be returned after calling suspend().
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*/
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if (task == XPIPE || task == XPOPEN) susp_count++;/* #procs susp'ed on pipe*/
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fp->fp_suspended = SUSPENDED;
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fp->fp_fd = m_in.fd << 8 | call_nr;
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fp->fp_task = -task;
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if (task == XLOCK) {
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fp->fp_buffer = (char *) m_in.name1; /* third arg to fcntl() */
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fp->fp_nbytes = m_in.request; /* second arg to fcntl() */
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} else {
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fp->fp_buffer = m_in.buffer; /* for reads and writes */
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fp->fp_nbytes = m_in.nbytes;
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}
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}
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/*===========================================================================*
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* release *
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*===========================================================================*/
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PUBLIC void release(ip, call_nr, count)
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register struct inode *ip; /* inode of pipe */
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int call_nr; /* READ, WRITE, OPEN or CREAT */
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int count; /* max number of processes to release */
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{
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/* Check to see if any process is hanging on the pipe whose inode is in 'ip'.
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* If one is, and it was trying to perform the call indicated by 'call_nr',
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* release it.
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*/
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register struct fproc *rp;
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/* Search the proc table. */
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for (rp = &fproc[0]; rp < &fproc[NR_PROCS]; rp++) {
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if (rp->fp_suspended == SUSPENDED &&
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rp->fp_revived == NOT_REVIVING &&
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(rp->fp_fd & BYTE) == call_nr &&
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rp->fp_filp[rp->fp_fd>>8]->filp_ino == ip) {
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revive((int)(rp - fproc), 0);
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susp_count--; /* keep track of who is suspended */
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if (--count == 0) return;
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}
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}
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}
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/*===========================================================================*
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* revive *
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*===========================================================================*/
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PUBLIC void revive(proc_nr, bytes)
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int proc_nr; /* process to revive */
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int bytes; /* if hanging on task, how many bytes read */
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{
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/* Revive a previously blocked process. When a process hangs on tty, this
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* is the way it is eventually released.
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*/
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register struct fproc *rfp;
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register int task;
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if (proc_nr < 0 || proc_nr >= NR_PROCS) panic("revive err", proc_nr);
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rfp = &fproc[proc_nr];
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if (rfp->fp_suspended == NOT_SUSPENDED || rfp->fp_revived == REVIVING)return;
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/* The 'reviving' flag only applies to pipes. Processes waiting for TTY get
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* a message right away. The revival process is different for TTY and pipes.
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* For TTY revival, the work is already done, for pipes it is not: the proc
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* must be restarted so it can try again.
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*/
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task = -rfp->fp_task;
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if (task == XPIPE || task == XLOCK) {
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/* Revive a process suspended on a pipe or lock. */
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rfp->fp_revived = REVIVING;
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reviving++; /* process was waiting on pipe or lock */
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} else {
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rfp->fp_suspended = NOT_SUSPENDED;
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if (task == XPOPEN) /* process blocked in open or create */
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reply(proc_nr, rfp->fp_fd>>8);
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else {
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/* Revive a process suspended on TTY or other device. */
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rfp->fp_nbytes = bytes; /*pretend it wants only what there is*/
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reply(proc_nr, bytes); /* unblock the process */
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}
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}
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}
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/*===========================================================================*
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* do_unpause *
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*===========================================================================*/
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PUBLIC int do_unpause()
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{
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/* A signal has been sent to a user who is paused on the file system.
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* Abort the system call with the EINTR error message.
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*/
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register struct fproc *rfp;
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int proc_nr, task, fild;
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struct filp *f;
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dev_t dev;
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message mess;
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if (who > PM_PROC_NR) return(EPERM);
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proc_nr = m_in.pro;
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if (proc_nr < 0 || proc_nr >= NR_PROCS) panic("unpause err 1", proc_nr);
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rfp = &fproc[proc_nr];
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if (rfp->fp_suspended == NOT_SUSPENDED) return(OK);
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task = -rfp->fp_task;
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switch (task) {
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case XPIPE: /* process trying to read or write a pipe */
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break;
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case XLOCK: /* process trying to set a lock with FCNTL */
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break;
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case XPOPEN: /* process trying to open a fifo */
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break;
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default: /* process trying to do device I/O (e.g. tty)*/
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fild = (rfp->fp_fd >> 8) & BYTE;/* extract file descriptor */
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if (fild < 0 || fild >= OPEN_MAX)panic("unpause err 2",NO_NUM);
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f = rfp->fp_filp[fild];
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dev = (dev_t) f->filp_ino->i_zone[0]; /* device hung on */
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mess.TTY_LINE = (dev >> MINOR) & BYTE;
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mess.PROC_NR = proc_nr;
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/* Tell kernel R or W. Mode is from current call, not open. */
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mess.COUNT = (rfp->fp_fd & BYTE) == READ ? R_BIT : W_BIT;
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mess.m_type = CANCEL;
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fp = rfp; /* hack - ctty_io uses fp */
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(*dmap[(dev >> MAJOR) & BYTE].dmap_io)(task, &mess);
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}
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rfp->fp_suspended = NOT_SUSPENDED;
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reply(proc_nr, EINTR); /* signal interrupted call */
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return(OK);
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}
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