/* This file deals with the suspension and revival of processes. A process can * be suspended because it wants to read or write from a pipe and can't, or * because it wants to read or write from a special file and can't. When a * process can't continue it is suspended, and revived later when it is able * to continue. * * The entry points into this file are * do_pipe: perform the PIPE system call * pipe_check: check to see that a read or write on a pipe is feasible now * suspend: suspend a process that cannot do a requested read or write * release: check to see if a suspended process can be released and do it * revive: mark a suspended process as able to run again * do_unpause: a signal has been sent to a process; see if it suspended */ #include "../h/const.h" #include "../h/type.h" #include "../h/callnr.h" #include "../h/com.h" #include "../h/error.h" #include "../h/signal.h" #include "const.h" #include "type.h" #include "file.h" #include "fproc.h" #include "glo.h" #include "inode.h" #include "param.h" PRIVATE message mess; /*===========================================================================* * do_pipe * *===========================================================================*/ PUBLIC int do_pipe() { /* Perform the pipe(fil_des) system call. */ register struct fproc *rfp; register struct inode *rip; int r; dev_nr device; struct filp *fil_ptr0, *fil_ptr1; int fil_des[2]; /* reply goes here */ extern struct inode *alloc_inode(); /* Acquire two file descriptors. */ rfp = fp; if ( (r = get_fd(R_BIT, &fil_des[0], &fil_ptr0)) != OK) return(r); rfp->fp_filp[fil_des[0]] = fil_ptr0; fil_ptr0->filp_count = 1; if ( (r = get_fd(W_BIT, &fil_des[1], &fil_ptr1)) != OK) { rfp->fp_filp[fil_des[0]] = NIL_FILP; fil_ptr0->filp_count = 0; return(r); } rfp->fp_filp[fil_des[1]] = fil_ptr1; fil_ptr1->filp_count = 1; /* Make the inode in the current working directory. */ device = rfp->fp_workdir->i_dev; /* inode dev is same as working dir */ if ( (rip = alloc_inode(device, I_REGULAR)) == NIL_INODE) { rfp->fp_filp[fil_des[0]] = NIL_FILP; fil_ptr0->filp_count = 0; rfp->fp_filp[fil_des[1]] = NIL_FILP; fil_ptr1->filp_count = 0; return(err_code); } rip->i_pipe = I_PIPE; fil_ptr0->filp_ino = rip; dup_inode(rip); /* for double usage */ fil_ptr1->filp_ino = rip; rw_inode(rip, WRITING); /* mark inode as allocated */ reply_i1 = fil_des[0]; reply_i2 = fil_des[1]; return(OK); } /*===========================================================================* * pipe_check * *===========================================================================*/ PUBLIC int pipe_check(rip, rw_flag, virgin, bytes, position) register struct inode *rip; /* the inode of the pipe */ int rw_flag; /* READING or WRITING */ int virgin; /* 1 if no data transferred yet, else 0 */ register int bytes; /* bytes to be read or written (all chunks) */ register file_pos *position; /* pointer to current file position */ { /* Pipes are a little different. If a process reads from an empty pipe for * which a writer still exists, suspend the reader. If the pipe is empty * and there is no writer, return 0 bytes. If a process is writing to a * pipe and no one is reading from it, give a broken pipe error. */ extern struct filp *find_filp(); /* If reading, check for empty pipe. */ if (rw_flag == READING) { if (*position >= rip->i_size) { /* Process is reading from an empty pipe. */ if (find_filp(rip, W_BIT) != NIL_FILP) { /* Writer exists; suspend rdr if no data already read.*/ if (virgin) suspend(XPIPE); /* block reader */ /* If need be, activate sleeping writer. */ if (susp_count > 0) release(rip, WRITE, 1); } return(0); } } else { /* Process is writing to a pipe. */ if (bytes > PIPE_SIZE) return(EFBIG); if (find_filp(rip, R_BIT) == NIL_FILP) { /* Tell MM to generate a SIGPIPE signal. */ mess.m_type = KSIG; mess.PROC1 = fp - fproc; mess.SIG_MAP = 1 << (SIGPIPE - 1); send(MM_PROC_NR, &mess); return(EPIPE); } if (*position + bytes > PIPE_SIZE) { suspend(XPIPE); /* stop writer -- pipe full */ return(0); } /* Writing to an empty pipe. Search for suspended reader. */ if (*position == 0) release(rip, READ, 1); } return(1); } /*===========================================================================* * suspend * *===========================================================================*/ PUBLIC suspend(task) int task; /* who is proc waiting for? (PIPE = pipe) */ { /* Take measures to suspend the processing of the present system call. * Store the parameters to be used upon resuming in the process table. * (Actually they are not used when a process is waiting for an I/O device, * but they are needed for pipes, and it is not worth making the distinction.) */ if (task == XPIPE) susp_count++; /* count procs suspended on pipe */ fp->fp_suspended = SUSPENDED; fp->fp_fd = fd << 8 | fs_call; fp->fp_buffer = buffer; fp->fp_nbytes = nbytes; fp->fp_task = -task; dont_reply = TRUE; /* do not send caller a reply message now */ } /*===========================================================================* * release * *===========================================================================*/ PUBLIC release(ip, call_nr, count) register struct inode *ip; /* inode of pipe */ int call_nr; /* READ or WRITE */ int count; /* max number of processes to release */ { /* Check to see if any process is hanging on the pipe whose inode is in 'ip'. * If one is, and it was trying to perform the call indicated by 'call_nr' * (READ or WRITE), release it. */ register struct fproc *rp; /* Search the proc table. */ for (rp = &fproc[0]; rp < &fproc[NR_PROCS]; rp++) { if (rp->fp_suspended == SUSPENDED && (rp->fp_fd & BYTE) == call_nr && rp->fp_filp[rp->fp_fd>>8]->filp_ino == ip) { revive(rp - fproc, 0); susp_count--; /* keep track of who is suspended */ if (--count == 0) return; } } } /*===========================================================================* * revive * *===========================================================================*/ PUBLIC revive(proc_nr, bytes) int proc_nr; /* process to revive */ int bytes; /* if hanging on task, how many bytes read */ { /* Revive a previously blocked process. When a process hangs on tty, this * is the way it is eventually released. */ register struct fproc *rfp; if (proc_nr < 0 || proc_nr >= NR_PROCS) panic("revive err", proc_nr); rfp = &fproc[proc_nr]; if (rfp->fp_suspended == NOT_SUSPENDED) return; /* The 'reviving' flag only applies to pipes. Processes waiting for TTY get * a message right away. The revival process is different for TTY and pipes. * For TTY revival, the work is already done, for pipes it is not: the proc * must be restarted so it can try again. */ if (rfp->fp_task == XPIPE) { /* Revive a process suspended on a pipe. */ rfp->fp_revived = REVIVING; reviving++; /* process was waiting on pipe */ } else { /* Revive a process suspended on TTY or other device. */ rfp->fp_suspended = NOT_SUSPENDED; rfp->fp_nbytes = bytes; /* pretend it only wants what there is */ reply(proc_nr, bytes); /* unblock the process */ } } /*===========================================================================* * do_unpause * *===========================================================================*/ PUBLIC int do_unpause() { /* A signal has been sent to a user who is paused on the file system. * Abort the system call with the EINTR error message. */ register struct fproc *rfp; int proc_nr, task; struct filp *f; dev_nr dev; extern struct filp *get_filp(); if (who > MM_PROC_NR) return(EPERM); proc_nr = pro; if (proc_nr < 0 || proc_nr >= NR_PROCS) panic("unpause err 1", proc_nr); rfp = &fproc[proc_nr]; if (rfp->fp_suspended == NOT_SUSPENDED) return(OK); task = -rfp->fp_task; if (task != XPIPE) { f = get_filp(rfp->fp_fd); dev = f->filp_ino->i_zone[0]; /* device on which proc is hanging */ mess.TTY_LINE = (dev >> MINOR) & BYTE; mess.PROC_NR = proc_nr; mess.m_type = CANCEL; if (sendrec(task, &mess) != OK) panic("unpause err 2", NO_NUM); while (mess.REP_PROC_NR != proc_nr) { revive(mess.REP_PROC_NR, mess.REP_STATUS); if (receive(task, &m) != OK) panic("unpause err 3", NO_NUM); } revive(proc_nr, EINTR); /* signal interrupted call */ } return(OK); }