minix3/servers/vfs/pipe.c

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2020-02-21 00:59:27 +05:30
/* 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_pipe2: perform the PIPE2 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
* unsuspend_by_endpt: revive all processes blocking on a given process
* do_unpause: a signal has been sent to a process; see if it suspended
*/
#include "fs.h"
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <assert.h>
#include <minix/callnr.h>
#include <minix/endpoint.h>
#include <minix/com.h>
#include <minix/u64.h>
#include <sys/select.h>
#include <sys/time.h>
#include "file.h"
#include "scratchpad.h"
#include <minix/vfsif.h>
#include "vnode.h"
#include "vmnt.h"
static int create_pipe(int fil_des[2], int flags);
/*===========================================================================*
* do_pipe2 *
*===========================================================================*/
int do_pipe2(void)
{
/* Perform the pipe2(fil_des[2], flags) system call. */
int r, flags;
int fil_des[2]; /* reply goes here */
flags = job_m_in.m_lc_vfs_pipe2.flags;
r = create_pipe(fil_des, flags);
if (r == OK) {
job_m_out.m_lc_vfs_pipe2.fd0 = fil_des[0];
job_m_out.m_lc_vfs_pipe2.fd1 = fil_des[1];
}
return r;
}
/*===========================================================================*
* create_pipe *
*===========================================================================*/
static int create_pipe(int fil_des[2], int flags)
{
register struct fproc *rfp;
int r;
struct filp *fil_ptr0, *fil_ptr1;
struct vnode *vp;
struct vmnt *vmp;
struct node_details res;
/* Get a lock on PFS */
if ((vmp = find_vmnt(PFS_PROC_NR)) == NULL) panic("PFS gone");
if ((r = lock_vmnt(vmp, VMNT_READ)) != OK) return(r);
/* See if a free vnode is available */
if ((vp = get_free_vnode()) == NULL) {
unlock_vmnt(vmp);
return(err_code);
}
lock_vnode(vp, VNODE_OPCL);
/* Acquire two file descriptors. */
rfp = fp;
if ((r = get_fd(fp, 0, R_BIT, &fil_des[0], &fil_ptr0)) != OK) {
unlock_vnode(vp);
unlock_vmnt(vmp);
return(r);
}
rfp->fp_filp[fil_des[0]] = fil_ptr0;
fil_ptr0->filp_count = 1; /* mark filp in use */
if ((r = get_fd(fp, 0, W_BIT, &fil_des[1], &fil_ptr1)) != OK) {
rfp->fp_filp[fil_des[0]] = NULL;
fil_ptr0->filp_count = 0; /* mark filp free */
unlock_filp(fil_ptr0);
unlock_vnode(vp);
unlock_vmnt(vmp);
return(r);
}
rfp->fp_filp[fil_des[1]] = fil_ptr1;
fil_ptr1->filp_count = 1;
/* Create a named pipe inode on PipeFS */
r = req_newnode(PFS_PROC_NR, fp->fp_effuid, fp->fp_effgid, I_NAMED_PIPE,
NO_DEV, &res);
if (r != OK) {
rfp->fp_filp[fil_des[0]] = NULL;
fil_ptr0->filp_count = 0;
rfp->fp_filp[fil_des[1]] = NULL;
fil_ptr1->filp_count = 0;
unlock_filp(fil_ptr1);
unlock_filp(fil_ptr0);
unlock_vnode(vp);
unlock_vmnt(vmp);
return(r);
}
/* Fill in vnode */
vp->v_fs_e = res.fs_e;
vp->v_mapfs_e = res.fs_e;
vp->v_inode_nr = res.inode_nr;
vp->v_mapinode_nr = res.inode_nr;
vp->v_mode = res.fmode;
vp->v_fs_count = 1;
vp->v_mapfs_count = 1;
vp->v_ref_count = 1;
vp->v_size = 0;
vp->v_vmnt = NULL;
vp->v_dev = NO_DEV;
/* Fill in filp objects */
fil_ptr0->filp_vno = vp;
dup_vnode(vp);
fil_ptr1->filp_vno = vp;
fil_ptr0->filp_flags = O_RDONLY | (flags & ~O_ACCMODE);
fil_ptr1->filp_flags = O_WRONLY | (flags & ~O_ACCMODE);
if (flags & O_CLOEXEC) {
FD_SET(fil_des[0], &rfp->fp_cloexec_set);
FD_SET(fil_des[1], &rfp->fp_cloexec_set);
}
unlock_filps(fil_ptr0, fil_ptr1);
unlock_vmnt(vmp);
return(OK);
}
/*===========================================================================*
* map_vnode *
*===========================================================================*/
int map_vnode(vp, map_to_fs_e)
struct vnode *vp;
endpoint_t map_to_fs_e;
{
int r;
struct vmnt *vmp;
struct node_details res;
if(vp->v_mapfs_e != NONE) return(OK); /* Already mapped; nothing to do. */
if ((vmp = find_vmnt(map_to_fs_e)) == NULL)
panic("Can't map to unknown endpoint");
if ((r = lock_vmnt(vmp, VMNT_WRITE)) != OK) {
if (r == EBUSY)
vmp = NULL; /* Already locked, do not unlock */
else
return(r);
}
/* Create a temporary mapping of this inode to another FS. Read and write
* operations on data will be handled by that FS. The rest by the 'original'
* FS that holds the inode. */
if ((r = req_newnode(map_to_fs_e, fp->fp_effuid, fp->fp_effgid, I_NAMED_PIPE,
vp->v_dev, &res)) == OK) {
vp->v_mapfs_e = res.fs_e;
vp->v_mapinode_nr = res.inode_nr;
vp->v_mapfs_count = 1;
}
if (vmp) unlock_vmnt(vmp);
return(r);
}
/*===========================================================================*
* pipe_check *
*===========================================================================*/
int pipe_check(
struct filp *filp, /* the filp of the pipe */
int rw_flag, /* READING or WRITING */
int oflags, /* flags set by open or fcntl */
int bytes, /* bytes to be read or written (all chunks) */
int notouch /* check only */
)
{
/* 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.
*/
struct vnode *vp;
off_t pos;
int r = OK;
vp = filp->filp_vno;
/* Reads start at the beginning; writes append to pipes */
if (notouch) /* In this case we don't actually care whether data transfer
* would succeed. See POSIX 1003.1-2008 */
pos = 0;
else if (rw_flag == READING)
pos = 0;
else {
pos = vp->v_size;
}
/* If reading, check for empty pipe. */
if (rw_flag == READING) {
if (vp->v_size == 0) {
/* Process is reading from an empty pipe. */
if (find_filp(vp, W_BIT) != NULL) {
/* Writer exists */
if (oflags & O_NONBLOCK)
r = EAGAIN;
else
r = SUSPEND;
/* If need be, activate sleeping writers. */
/* We ignore notouch voluntary here. */
if (susp_count > 0)
release(vp, VFS_WRITE, susp_count);
}
return(r);
}
return(bytes);
}
/* Process is writing to a pipe. */
if (find_filp(vp, R_BIT) == NULL) {
return(EPIPE);
}
/* Calculate how many bytes can be written. */
if (pos + bytes > PIPE_BUF) {
if (oflags & O_NONBLOCK) {
if (bytes <= PIPE_BUF) {
/* Write has to be atomic */
return(EAGAIN);
}
/* Compute available space */
bytes = PIPE_BUF - pos;
if (bytes > 0) {
/* Do a partial write. Need to wakeup reader */
if (!notouch)
release(vp, VFS_READ, susp_count);
return(bytes);
} else {
/* Pipe is full */
return(EAGAIN);
}
}
if (bytes > PIPE_BUF) {
/* Compute available space */
bytes = PIPE_BUF - pos;
if (bytes > 0) {
/* Do a partial write. Need to wakeup reader
* since we'll suspend ourself in read_write()
*/
if (!notouch)
release(vp, VFS_READ, susp_count);
return(bytes);
}
}
/* Pipe is full */
return(SUSPEND);
}
/* Writing to an empty pipe. Search for suspended reader. */
if (pos == 0 && !notouch)
release(vp, VFS_READ, susp_count);
/* Requested amount fits */
return(bytes);
}
/*===========================================================================*
* suspend *
*===========================================================================*/
void suspend(int why)
{
/* 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.)
* The SUSPEND pseudo error should be returned after calling suspend().
*/
if (why == FP_BLOCKED_ON_POPEN || why == FP_BLOCKED_ON_PIPE)
/* #procs susp'ed on pipe*/
susp_count++;
fp->fp_blocked_on = why;
assert(fp->fp_grant == GRANT_INVALID || !GRANT_VALID(fp->fp_grant));
fp->fp_block_callnr = job_call_nr;
}
/*===========================================================================*
* wait_for *
*===========================================================================*/
void wait_for(endpoint_t who)
{
if(who == NONE || who == ANY)
panic("suspend on NONE or ANY");
suspend(FP_BLOCKED_ON_OTHER);
fp->fp_task = who;
}
/*===========================================================================*
* pipe_suspend *
*===========================================================================*/
void pipe_suspend(filp, buf, size)
struct filp *filp;
vir_bytes buf;
size_t size;
{
/* Take measures to suspend the processing of the present system call.
* Store the parameters to be used upon resuming in the process table.
*/
scratch(fp).file.filp = filp;
scratch(fp).io.io_buffer = buf;
scratch(fp).io.io_nbytes = size;
suspend(FP_BLOCKED_ON_PIPE);
}
/*===========================================================================*
* unsuspend_by_endpt *
*===========================================================================*/
void unsuspend_by_endpt(endpoint_t proc_e)
{
/* Revive processes waiting for drivers (SUSPENDed) that have disappeared with
* return code EAGAIN.
*/
struct fproc *rp;
for (rp = &fproc[0]; rp < &fproc[NR_PROCS]; rp++) {
if (rp->fp_pid == PID_FREE) continue;
if (rp->fp_blocked_on == FP_BLOCKED_ON_OTHER && rp->fp_task == proc_e)
revive(rp->fp_endpoint, EIO);
}
/* Revive processes waiting in drivers on select()s with EAGAIN too */
select_unsuspend_by_endpt(proc_e);
return;
}
/*===========================================================================*
* release *
*===========================================================================*/
void release(vp, op, count)
register struct vnode *vp; /* inode of pipe */
int op; /* VFS_READ, VFS_WRITE, or VFS_OPEN */
int count; /* max number of processes to release */
{
/* Check to see if any process is hanging on vnode 'vp'. If one is, and it
* was trying to perform the call indicated by 'op', release it.
*/
register struct fproc *rp;
struct filp *f;
int selop;
/* Trying to perform the call also includes SELECTing on it with that
* operation.
*/
if (op == VFS_READ || op == VFS_WRITE) {
if (op == VFS_READ)
selop = SEL_RD;
else
selop = SEL_WR;
for (f = &filp[0]; f < &filp[NR_FILPS]; f++) {
if (f->filp_count < 1 || !(f->filp_pipe_select_ops & selop) ||
f->filp_vno != vp)
continue;
select_callback(f, selop);
f->filp_pipe_select_ops &= ~selop;
}
}
/* Search the proc table. */
for (rp = &fproc[0]; rp < &fproc[NR_PROCS] && count > 0; rp++) {
if (rp->fp_pid != PID_FREE && fp_is_blocked(rp) &&
!(rp->fp_flags & FP_REVIVED) && rp->fp_block_callnr == op) {
/* Find the vnode. Depending on the reason the process was
* suspended, there are different ways of finding it.
*/
if (rp->fp_blocked_on == FP_BLOCKED_ON_POPEN ||
rp->fp_blocked_on == FP_BLOCKED_ON_LOCK ||
rp->fp_blocked_on == FP_BLOCKED_ON_OTHER) {
f = rp->fp_filp[scratch(rp).file.fd_nr];
if (f == NULL || f->filp_mode == FILP_CLOSED)
continue;
if (rp->fp_filp[scratch(rp).file.fd_nr]->filp_vno != vp)
continue;
} else if (rp->fp_blocked_on == FP_BLOCKED_ON_PIPE) {
if (scratch(rp).file.filp == NULL)
continue;
if (scratch(rp).file.filp->filp_vno != vp)
continue;
} else
continue;
/* We found the vnode. Revive process. */
revive(rp->fp_endpoint, 0);
susp_count--; /* keep track of who is suspended */
if(susp_count < 0)
panic("susp_count now negative: %d", susp_count);
if (--count == 0) return;
}
}
}
/*===========================================================================*
* revive *
*===========================================================================*/
void revive(endpoint_t proc_e, int returned)
{
/* Revive a previously blocked process. When a process hangs on tty, this
* is the way it is eventually released. For processes blocked on _SELECT and
* _OTHER, this function MUST NOT block its calling thread.
*/
struct fproc *rfp;
int blocked_on;
int fd_nr, slot;
if (proc_e == NONE || isokendpt(proc_e, &slot) != OK) return;
rfp = &fproc[slot];
if (!fp_is_blocked(rfp) || (rfp->fp_flags & FP_REVIVED)) 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 select and TTY revival, the work is already done, for pipes it is not:
* the proc must be restarted so it can try again.
*/
blocked_on = rfp->fp_blocked_on;
fd_nr = scratch(rfp).file.fd_nr;
if (blocked_on == FP_BLOCKED_ON_PIPE || blocked_on == FP_BLOCKED_ON_LOCK) {
/* Revive a process suspended on a pipe or lock. */
rfp->fp_flags |= FP_REVIVED;
reviving++; /* process was waiting on pipe or lock */
} else {
rfp->fp_blocked_on = FP_BLOCKED_ON_NONE;
scratch(rfp).file.fd_nr = 0;
if (blocked_on == FP_BLOCKED_ON_POPEN) {
/* process blocked in open or create */
replycode(proc_e, fd_nr);
} else if (blocked_on == FP_BLOCKED_ON_SELECT) {
replycode(proc_e, returned);
} else {
/* Revive a process suspended on TTY or other device.
* Pretend it wants only what there is.
*/
scratch(rfp).io.io_nbytes = returned;
/* If a grant has been issued by FS for this I/O, revoke
* it again now that I/O is done.
*/
if (GRANT_VALID(rfp->fp_grant)) {
if(cpf_revoke(rfp->fp_grant)) {
panic("VFS: revoke failed for grant: %d",
rfp->fp_grant);
}
rfp->fp_grant = GRANT_INVALID;
}
replycode(proc_e, returned);/* unblock the process */
}
}
}
/*===========================================================================*
* unpause *
*===========================================================================*/
void unpause(void)
{
/* A signal has been sent to a user who is paused on the file system.
* Abort the system call with the EINTR error message.
*/
int blocked_on, fild, status = EINTR;
struct filp *f;
dev_t dev;
int wasreviving = 0;
if (!fp_is_blocked(fp)) return;
blocked_on = fp->fp_blocked_on;
/* Clear the block status now. The procedure below might make blocking calls
* and it is imperative that while at least cdev_cancel() is executing, other
* parts of VFS do not perceive this process as blocked on something.
*/
fp->fp_blocked_on = FP_BLOCKED_ON_NONE;
if (fp->fp_flags & FP_REVIVED) {
fp->fp_flags &= ~FP_REVIVED;
reviving--;
wasreviving = 1;
}
switch (blocked_on) {
case FP_BLOCKED_ON_PIPE:/* process trying to read or write a pipe */
/* If the operation succeeded partially, return the bytes
* processed so far, and clear the remembered state. Otherwise,
* return EINTR as usual.
*/
if (fp->fp_cum_io_partial > 0) {
status = fp->fp_cum_io_partial;
fp->fp_cum_io_partial = 0;
}
break;
case FP_BLOCKED_ON_LOCK:/* process trying to set a lock with FCNTL */
break;
case FP_BLOCKED_ON_SELECT:/* process blocking on select() */
select_forget();
break;
case FP_BLOCKED_ON_POPEN: /* process trying to open a fifo */
break;
case FP_BLOCKED_ON_OTHER:/* process trying to do device I/O (e.g. tty)*/
fild = scratch(fp).file.fd_nr;
if (fild < 0 || fild >= OPEN_MAX)
panic("file descriptor out-of-range");
f = fp->fp_filp[fild];
if(!f) {
sys_diagctl_stacktrace(fp->fp_endpoint);
panic("process %d blocked on empty fd %d",
fp->fp_endpoint, fild);
}
dev = f->filp_vno->v_sdev; /* device hung on */
status = cdev_cancel(dev);
break;
default :
panic("VFS: unknown block reason: %d", blocked_on);
}
if ((blocked_on == FP_BLOCKED_ON_PIPE || blocked_on == FP_BLOCKED_ON_POPEN)&&
!wasreviving) {
susp_count--;
}
replycode(fp->fp_endpoint, status); /* signal interrupted call */
}