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minix/servers/avfs/pipe.c
Thomas Veerman de5a9a3e8b AVFS: Use scratchpad instead of m_in to pass around file descriptors 
Some code relies on having the file descriptor in m_in.fd. Consequently,
m_in is not only used to provide syscall parameters from user space to
VFS, but also as a global variable to store temporary data within VFS.
This has the ugly side effect that m_in gets overwritten during core
dumping.*

To work around this problem VFS now uses a so called "scratchpad" to
store temporary data that has to be globally accessible. This is a simple
table indexed by process number, just like fproc. The scratchpad allows
us to store the buffer pointer and buffer size for suspended system calls
(i.e., read, write, open, lock) instead of using fproc. This makes fproc
a bit smaller and fproc iterators a bit faster. Moreover, suspension of
processes becomes simpler altogether and suspended operations on pipes
are now less of a special case.

* This patch fixes a bug where due to unexpected m_in overwriting a
coredump would fail, and consequently resources are leaked. The coredump
was triggered with:
$ a() { a; }
$ a
2011-12-21 10:52:51 +00:00

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/* 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
* 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 <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 "fproc.h"
#include "scratchpad.h"
#include "dmap.h"
#include "param.h"
#include "select.h"
#include <minix/vfsif.h>
#include "vnode.h"
#include "vmnt.h"
/*===========================================================================*
* do_pipe *
*===========================================================================*/
PUBLIC int do_pipe()
{
/* Perform the pipe(fil_des) system call. */
register struct fproc *rfp;
int r;
struct filp *fil_ptr0, *fil_ptr1;
int fil_des[2]; /* reply goes here */
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_WRITE)) != OK) return(r);
/* See if a free vnode is available */
if ((vp = get_free_vnode()) == NULL) return(err_code);
lock_vnode(vp, VNODE_OPCL);
/* Acquire two file descriptors. */
rfp = fp;
if ((r = get_fd(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;
FD_SET(fil_des[0], &rfp->fp_filp_inuse);
fil_ptr0->filp_count = 1; /* mark filp in use */
if ((r = get_fd(0, W_BIT, &fil_des[1], &fil_ptr1)) != OK) {
rfp->fp_filp[fil_des[0]] = NULL;
FD_CLR(fil_des[0], &rfp->fp_filp_inuse);
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;
FD_SET(fil_des[1], &rfp->fp_filp_inuse);
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;
FD_CLR(fil_des[0], &rfp->fp_filp_inuse);
fil_ptr0->filp_count = 0;
rfp->fp_filp[fil_des[1]] = NULL;
FD_CLR(fil_des[1], &rfp->fp_filp_inuse);
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_pipe = I_PIPE;
vp->v_pipe_rd_pos= 0;
vp->v_pipe_wr_pos= 0;
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;
fil_ptr1->filp_flags = O_WRONLY;
m_out.reply_i1 = fil_des[0];
m_out.reply_i2 = fil_des[1];
unlock_filps(fil_ptr0, fil_ptr1);
unlock_vmnt(vmp);
return(OK);
}
/*===========================================================================*
* map_vnode *
*===========================================================================*/
PUBLIC 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 *
*===========================================================================*/
PUBLIC int pipe_check(vp, rw_flag, oflags, bytes, position, notouch)
register struct vnode *vp; /* the inode of the pipe */
int rw_flag; /* READING or WRITING */
int oflags; /* flags set by open or fcntl */
register int bytes; /* bytes to be read or written (all chunks) */
u64_t position; /* current file position */
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.
*/
off_t pos;
int r = OK;
if (ex64hi(position) != 0)
panic("pipe_check: position too large in pipe");
pos = ex64lo(position);
/* If reading, check for empty pipe. */
if (rw_flag == READING) {
if (pos >= vp->v_size) {
/* 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. */
if (susp_count > 0)
release(vp, WRITE, susp_count);
}
return(r);
}
return(bytes);
}
/* Process is writing to a pipe. */
if (find_filp(vp, R_BIT) == NULL) {
/* Process is writing, but there is no reader. Tell kernel to generate
* a SIGPIPE signal. */
if (!notouch) sys_kill(fp->fp_endpoint, SIGPIPE);
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, 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, 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, READ, susp_count);
/* Requested amount fits */
return(bytes);
}
/*===========================================================================*
* suspend *
*===========================================================================*/
PUBLIC 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 DO_SANITYCHECKS
if(fp_is_blocked(fp))
panic("suspend: called for suspended process");
if(why == FP_BLOCKED_ON_NONE)
panic("suspend: called for FP_BLOCKED_ON_NONE");
#endif
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 = call_nr;
fp->fp_flags &= ~FP_SUSP_REOPEN; /* Clear this flag. The caller
* can set it when needed.
*/
}
/*===========================================================================*
* wait_for *
*===========================================================================*/
PUBLIC 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 *
*===========================================================================*/
PUBLIC void pipe_suspend(filp, buf, size)
struct filp *filp;
char *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.
*/
#if DO_SANITYCHECKS
if(fp_is_blocked(fp))
panic("pipe_suspend: called for suspended process");
#endif
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 *
*===========================================================================*/
PUBLIC 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, EAGAIN);
}
/* Revive processes waiting in drivers on select()s with EAGAIN too */
select_unsuspend_by_endpt(proc_e);
return;
}
/*===========================================================================*
* release *
*===========================================================================*/
PUBLIC void release(vp, op, count)
register struct vnode *vp; /* inode of pipe */
int op; /* READ, WRITE, OPEN or CREAT */
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 'call_nr', 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 == READ || op == WRITE) {
if (op == 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_DOPEN ||
rp->fp_blocked_on == FP_BLOCKED_ON_LOCK ||
rp->fp_blocked_on == FP_BLOCKED_ON_OTHER) {
if (!FD_ISSET(scratch(rp).file.fd_nr,
&rp->fp_filp_inuse))
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 *
*===========================================================================*/
PUBLIC void revive(proc_nr_e, returned)
int proc_nr_e; /* process to revive */
int returned; /* 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;
int blocked_on;
int fd_nr, slot;
struct filp *fil_ptr;
if (proc_nr_e == NONE || isokendpt(proc_nr_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 if (blocked_on == FP_BLOCKED_ON_DOPEN) {
rfp->fp_blocked_on = FP_BLOCKED_ON_NONE;
scratch(rfp).file.fd_nr = 0;
if (returned < 0) {
fil_ptr = rfp->fp_filp[fd_nr];
lock_filp(fil_ptr, VNODE_OPCL);
rfp->fp_filp[fd_nr] = NULL;
FD_CLR(fd_nr, &rfp->fp_filp_inuse);
if (fil_ptr->filp_count != 1) {
panic("VFS: revive: bad count in filp: %d",
fil_ptr->filp_count);
}
fil_ptr->filp_count = 0;
unlock_filp(fil_ptr);
put_vnode(fil_ptr->filp_vno);
fil_ptr->filp_vno = NULL;
reply(proc_nr_e, returned);
} else {
reply(proc_nr_e, fd_nr);
}
} 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 */
reply(proc_nr_e, fd_nr);
} else if (blocked_on == FP_BLOCKED_ON_SELECT) {
reply(proc_nr_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;
}
reply(proc_nr_e, returned); /* unblock the process */
}
}
}
/*===========================================================================*
* unpause *
*===========================================================================*/
PUBLIC void unpause(proc_nr_e)
int proc_nr_e;
{
/* 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, *org_fp;
int slot, blocked_on, fild, status = EINTR, major_dev, minor_dev;
struct filp *f;
dev_t dev;
message mess;
int wasreviving = 0;
if (isokendpt(proc_nr_e, &slot) != OK) {
printf("VFS: ignoring unpause for bogus endpoint %d\n", proc_nr_e);
return;
}
rfp = &fproc[slot];
if (!fp_is_blocked(rfp)) return;
blocked_on = rfp->fp_blocked_on;
if (rfp->fp_flags & FP_REVIVED) {
rfp->fp_flags &= ~FP_REVIVED;
reviving--;
wasreviving = 1;
}
switch (blocked_on) {
case FP_BLOCKED_ON_PIPE:/* process trying to read or write a pipe */
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(proc_nr_e);
break;
case FP_BLOCKED_ON_POPEN: /* process trying to open a fifo */
break;
case FP_BLOCKED_ON_DOPEN:/* process trying to open a device */
/* Don't cancel OPEN. Just wait until the open completes. */
return;
case FP_BLOCKED_ON_OTHER:/* process trying to do device I/O (e.g. tty)*/
if (rfp->fp_flags & FP_SUSP_REOPEN) {
/* Process is suspended while waiting for a reopen.
* Just reply EINTR.
*/
rfp->fp_flags &= ~FP_SUSP_REOPEN;
status = EINTR;
break;
}
fild = scratch(rfp).file.fd_nr;
if (fild < 0 || fild >= OPEN_MAX)
panic("file descriptor out-of-range");
f = rfp->fp_filp[fild];
dev = (dev_t) f->filp_vno->v_sdev; /* device hung on */
major_dev = major(dev);
minor_dev = minor(dev);
mess.TTY_LINE = minor_dev;
mess.USER_ENDPT = rfp->fp_ioproc;
mess.IO_GRANT = (char *) rfp->fp_grant;
/* Tell kernel R or W. Mode is from current call, not open. */
mess.COUNT = rfp->fp_block_callnr == READ ? R_BIT : W_BIT;
mess.m_type = CANCEL;
org_fp = fp;
fp = rfp; /* hack - ctty_io uses fp */
(*dmap[major_dev].dmap_io)(rfp->fp_task, &mess);
fp = org_fp;
status = mess.REP_STATUS;
if (status == SUSPEND)
return; /* Process will be revived at a
* later time.
*/
if (status == EAGAIN) status = EINTR;
if (GRANT_VALID(rfp->fp_grant)) {
(void) cpf_revoke(rfp->fp_grant);
rfp->fp_grant = GRANT_INVALID;
}
break;
default :
panic("VFS: unknown block reason: %d", blocked_on);
}
rfp->fp_blocked_on = FP_BLOCKED_ON_NONE;
if ((blocked_on == FP_BLOCKED_ON_PIPE || blocked_on == FP_BLOCKED_ON_POPEN)&&
!wasreviving) {
susp_count--;
}
reply(proc_nr_e, status); /* signal interrupted call */
}
#if DO_SANITYCHECKS
/*===========================================================================*
* check_pipe *
*===========================================================================*/
PUBLIC int check_pipe(void)
{
/* Integrity check; verify that susp_count equals what the fproc table thinks
* is suspended on a pipe */
struct fproc *rfp;
int count = 0;
for (rfp = &fproc[0]; rfp < &fproc[NR_PROCS]; rfp++) {
if (rfp->fp_pid == PID_FREE) continue;
if ( !(rfp->fp_flags & FP_REVIVED) &&
(rfp->fp_blocked_on == FP_BLOCKED_ON_PIPE ||
rfp->fp_blocked_on == FP_BLOCKED_ON_POPEN)) {
count++;
}
}
if (count != susp_count) {
printf("check_pipe: count %d susp_count %d\n", count, susp_count);
return(0);
}
return(l);
}
#endif
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