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minix/minix/servers/vfs/select.c
David van Moolenbroek de95c84d3e VFS: fix short select(2) timeouts 
Some select queries require a response from device drivers.  If a
select call is nonblocking (with a zero timeout), the response to
the caller may have to be deferred until all involved drivers have
responded to the initial query.  This is handled just fine.

However, if the select call has a timeout that is so short that it
triggers before all the involved drivers have responded, the
resulting alarm would be discarded, possibly resulting in the call
blocking forever.  This fix changes the alarm handler such that if
the alarm triggers too early, the select call is further handled
as though it was nonblocking.

This fix resolves a test77 deadlock on really slow systems.

Change-Id: Ib487c8fe436802c3e11c57355ae0c8480721f06e
2015-09-16 10:41:46 +00:00

1106 lines
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/* Implement entry point to select system call.
*
* The entry points into this file are
* do_select: perform the SELECT system call
* select_callback: notify select system of possible fd operation
* select_unsuspend_by_endpt: cancel a blocking select on exiting driver
*
* The select code uses minimal locking, so that the replies from character
* drivers can be processed without blocking. Filps are locked only for pipes.
* We make the assumption that any other structures and fields are safe to
* check (and possibly change) as long as we know that a process is blocked on
* a select(2) call, meaning that all involved filps are guaranteed to stay
* open until either we finish the select call, it the process gets interrupted
* by a signal.
*/
#include "fs.h"
#include <sys/fcntl.h>
#include <sys/time.h>
#include <sys/select.h>
#include <sys/stat.h>
#include <minix/callnr.h>
#include <minix/u64.h>
#include <string.h>
#include <assert.h>
#include "file.h"
#include "vnode.h"
/* max. number of simultaneously pending select() calls */
#define MAXSELECTS 25
#define FROM_PROC 0
#define TO_PROC 1
static struct selectentry {
struct fproc *requestor; /* slot is free iff this is NULL */
endpoint_t req_endpt;
fd_set readfds, writefds, errorfds;
fd_set ready_readfds, ready_writefds, ready_errorfds;
fd_set *vir_readfds, *vir_writefds, *vir_errorfds;
struct filp *filps[OPEN_MAX];
int type[OPEN_MAX];
int nfds, nreadyfds;
int error;
char block;
char starting;
clock_t expiry;
minix_timer_t timer; /* if expiry > 0 */
} selecttab[MAXSELECTS];
static int copy_fdsets(struct selectentry *se, int nfds, int direction);
static void filp_status(struct filp *fp, int status);
static int is_deferred(struct selectentry *se);
static void restart_proc(struct selectentry *se);
static void ops2tab(int ops, int fd, struct selectentry *e);
static int is_regular_file(struct filp *f);
static int is_pipe(struct filp *f);
static int is_char_device(struct filp *f);
static void select_lock_filp(struct filp *f, int ops);
static int select_request_file(struct filp *f, int *ops, int block,
struct fproc *rfp);
static int select_request_char(struct filp *f, int *ops, int block,
struct fproc *rfp);
static int select_request_pipe(struct filp *f, int *ops, int block,
struct fproc *rfp);
static void select_cancel_all(struct selectentry *e);
static void select_cancel_filp(struct filp *f);
static void select_return(struct selectentry *);
static void select_restart_filps(void);
static int tab2ops(int fd, struct selectentry *e);
static void wipe_select(struct selectentry *s);
static struct fdtype {
int (*select_request)(struct filp *, int *ops, int block,
struct fproc *rfp);
int (*type_match)(struct filp *f);
} fdtypes[] = {
{ select_request_char, is_char_device },
{ select_request_file, is_regular_file },
{ select_request_pipe, is_pipe },
};
#define SEL_FDS (sizeof(fdtypes) / sizeof(fdtypes[0]))
/*===========================================================================*
* do_select *
*===========================================================================*/
int do_select(void)
{
/* Implement the select(nfds, readfds, writefds, errorfds, timeout) system
* call. First we copy the arguments and verify their sanity. Then we check
* whether there are file descriptors that satisfy the select call right off
* the bat. If so, or if there are no ready file descriptors but the process
* requested to return immediately, we return the result. Otherwise we set a
* timeout and wait for either the file descriptors to become ready or the
* timer to go off. If no timeout value was provided, we wait indefinitely.
*/
int r, nfds, do_timeout = 0, fd, s;
struct filp *f;
unsigned int type, ops;
struct timeval timeout;
struct selectentry *se;
vir_bytes vtimeout;
nfds = job_m_in.m_lc_vfs_select.nfds;
vtimeout = job_m_in.m_lc_vfs_select.timeout;
/* Sane amount of file descriptors? */
if (nfds < 0 || nfds > OPEN_MAX) return(EINVAL);
/* Find a slot to store this select request */
for (s = 0; s < MAXSELECTS; s++)
if (selecttab[s].requestor == NULL) /* Unused slot */
break;
if (s >= MAXSELECTS) return(ENOSPC);
se = &selecttab[s];
wipe_select(se); /* Clear results of previous usage */
se->requestor = fp;
se->req_endpt = who_e;
se->vir_readfds = job_m_in.m_lc_vfs_select.readfds;
se->vir_writefds = job_m_in.m_lc_vfs_select.writefds;
se->vir_errorfds = job_m_in.m_lc_vfs_select.errorfds;
/* Copy fdsets from the process */
if ((r = copy_fdsets(se, nfds, FROM_PROC)) != OK) {
se->requestor = NULL;
return(r);
}
/* Did the process set a timeout value? If so, retrieve it. */
if (vtimeout != 0) {
do_timeout = 1;
r = sys_datacopy_wrapper(who_e, vtimeout, SELF, (vir_bytes) &timeout,
sizeof(timeout));
if (r != OK) {
se->requestor = NULL;
return(r);
}
}
/* No nonsense in the timeval */
if (do_timeout && (timeout.tv_sec < 0 || timeout.tv_usec < 0)) {
se->requestor = NULL;
return(EINVAL);
}
/* If there is no timeout, we block forever. Otherwise, we block up to the
* specified time interval.
*/
if (!do_timeout) /* No timeout value set */
se->block = 1;
else if (do_timeout && (timeout.tv_sec > 0 || timeout.tv_usec > 0))
se->block = 1;
else /* timeout set as (0,0) - this effects a poll */
se->block = 0;
se->expiry = 0; /* no timer set (yet) */
/* We are going to lock filps, and that means that while locking a second
* filp, we might already get the results for the first one. In that case,
* the incoming results must not cause the select call to finish prematurely.
*/
se->starting = TRUE;
/* Verify that file descriptors are okay to select on */
for (fd = 0; fd < nfds; fd++) {
/* Because the select() interface implicitly includes file descriptors
* you might not want to select on, we have to figure out whether we're
* interested in them. Typically, these file descriptors include fd's
* inherited from the parent proc and file descriptors that have been
* close()d, but had a lower fd than one in the current set.
*/
if (!(ops = tab2ops(fd, se)))
continue; /* No operations set; nothing to do for this fd */
/* Get filp belonging to this fd */
f = se->filps[fd] = get_filp(fd, VNODE_READ);
if (f == NULL) {
if (err_code == EBADF)
r = err_code;
else /* File descriptor is 'ready' to return EIO */
r = EINTR;
se->requestor = NULL;
return(r);
}
/* Check file types. According to POSIX 2008:
* "The pselect() and select() functions shall support regular files,
* terminal and pseudo-terminal devices, FIFOs, pipes, and sockets. The
* behavior of pselect() and select() on file descriptors that refer to
* other types of file is unspecified."
*
* In our case, terminal and pseudo-terminal devices are handled by the
* TTY major and sockets by either INET major (socket type AF_INET) or
* UDS major (socket type AF_UNIX). Additionally, we give other
* character drivers the chance to handle select for any of their
* device nodes. Some may not implement support for select and let
* libchardriver return EBADF, which we then pass to the calling
* process once we receive the reply.
*/
se->type[fd] = -1;
for (type = 0; type < SEL_FDS; type++) {
if (fdtypes[type].type_match(f)) {
se->type[fd] = type;
se->nfds = fd+1;
se->filps[fd]->filp_selectors++;
break;
}
}
unlock_filp(f);
if (se->type[fd] == -1) { /* Type not found */
se->requestor = NULL;
return(EBADF);
}
}
/* Check all file descriptors in the set whether one is 'ready' now */
for (fd = 0; fd < nfds; fd++) {
/* Again, check for involuntarily selected fd's */
if (!(ops = tab2ops(fd, se)))
continue; /* No operations set; nothing to do for this fd */
/* File descriptors selected for reading that are not opened for
* reading should be marked as readable, as read calls would fail
* immediately. The same applies to writing.
*/
f = se->filps[fd];
if ((ops & SEL_RD) && !(f->filp_mode & R_BIT)) {
ops2tab(SEL_RD, fd, se);
ops &= ~SEL_RD;
}
if ((ops & SEL_WR) && !(f->filp_mode & W_BIT)) {
ops2tab(SEL_WR, fd, se);
ops &= ~SEL_WR;
}
/* Test filp for select operations if not already done so. e.g.,
* processes sharing a filp and both doing a select on that filp. */
if ((f->filp_select_ops & ops) != ops) {
int wantops;
wantops = (f->filp_select_ops |= ops);
type = se->type[fd];
select_lock_filp(f, wantops);
r = fdtypes[type].select_request(f, &wantops, se->block, fp);
unlock_filp(f);
if (r != OK && r != SUSPEND) {
se->error = r;
break; /* Error or bogus return code; abort */
}
/* The select request above might have turned on/off some
* operations because they were 'ready' or not meaningful.
* Either way, we might have a result and we need to store them
* in the select table entry. */
if (wantops & ops) ops2tab(wantops, fd, se);
}
}
/* At this point there won't be any blocking calls anymore. */
se->starting = FALSE;
if ((se->nreadyfds > 0 || se->error != OK || !se->block) &&
!is_deferred(se)) {
/* An error occurred, or fd's were found that were ready to go right
* away, and/or we were instructed not to block at all. Must return
* immediately. Do not copy FD sets if an error occurred.
*/
if (se->error != OK)
r = se->error;
else
r = copy_fdsets(se, se->nfds, TO_PROC);
select_cancel_all(se);
se->requestor = NULL;
if (r != OK)
return(r);
return(se->nreadyfds);
}
/* Convert timeval to ticks and set the timer. If it fails, undo
* all, return error.
*/
if (do_timeout) {
int ticks;
/* Open Group:
* "If the requested timeout interval requires a finer
* granularity than the implementation supports, the
* actual timeout interval shall be rounded up to the next
* supported value."
*/
#define USECPERSEC 1000000
while(timeout.tv_usec >= USECPERSEC) {
/* this is to avoid overflow with *system_hz below */
timeout.tv_usec -= USECPERSEC;
timeout.tv_sec++;
}
ticks = timeout.tv_sec * system_hz +
(timeout.tv_usec * system_hz + USECPERSEC-1) / USECPERSEC;
se->expiry = ticks;
set_timer(&se->timer, ticks, select_timeout_check, s);
}
/* process now blocked */
suspend(FP_BLOCKED_ON_SELECT);
return(SUSPEND);
}
/*===========================================================================*
* is_deferred *
*===========================================================================*/
static int is_deferred(struct selectentry *se)
{
/* Find out whether this select has pending initial replies */
int fd;
struct filp *f;
/* The select call must have finished its initialization at all. */
if (se->starting) return(TRUE);
for (fd = 0; fd < se->nfds; fd++) {
if ((f = se->filps[fd]) == NULL) continue;
if (f->filp_select_flags & (FSF_UPDATE|FSF_BUSY)) return(TRUE);
}
return(FALSE);
}
/*===========================================================================*
* is_regular_file *
*===========================================================================*/
static int is_regular_file(struct filp *f)
{
return(f && f->filp_vno && S_ISREG(f->filp_vno->v_mode));
}
/*===========================================================================*
* is_pipe *
*===========================================================================*/
static int is_pipe(struct filp *f)
{
/* Recognize either anonymous pipe or named pipe (FIFO) */
return(f && f->filp_vno && S_ISFIFO(f->filp_vno->v_mode));
}
/*===========================================================================*
* is_char_device *
*===========================================================================*/
static int is_char_device(struct filp *f)
{
/* See if this filp is a handle on a character device. This function MUST NOT
* block its calling thread. The given filp may or may not be locked.
*/
return (f && f->filp_vno && S_ISCHR(f->filp_vno->v_mode));
}
/*===========================================================================*
* select_request_char *
*===========================================================================*/
static int select_request_char(struct filp *f, int *ops, int block,
struct fproc *rfp)
{
/* Check readiness status on a character device. Unless suitable results are
* available right now, this will only initiate the polling process, causing
* result processing to be deferred. This function MUST NOT block its calling
* thread. The given filp may or may not be locked.
*/
dev_t dev;
int r, rops;
struct dmap *dp;
/* Start by remapping the device node number to a "real" device number. Those
* two are different only for CTTY_MAJOR aka /dev/tty, but that one single
* exception requires quite some extra effort here: the select code matches
* character driver replies to their requests based on the device number, so
* it needs to be aware that device numbers may be mapped. The idea is to
* perform the mapping once and store the result in the filp object, so that
* at least we don't run into problems when a process loses its controlling
* terminal while doing a select (see also free_proc). It should be noted
* that it is possible that multiple processes share the same /dev/tty filp,
* and they may not all have a controlling terminal. The ctty-less processes
* should never pass the mapping; a more problematic case is checked below.
*
* The cdev_map call also checks the major number for rough validity, so that
* we can use it to index the dmap array safely a bit later.
*/
if ((dev = cdev_map(f->filp_vno->v_sdev, rfp)) == NO_DEV)
return(ENXIO);
if (f->filp_char_select_dev != NO_DEV && f->filp_char_select_dev != dev) {
/* Currently, this case can occur as follows: a process with a
* controlling terminal opens /dev/tty and forks, the new child starts
* a new session, opens a new controlling terminal, and both parent and
* child call select on the /dev/tty file descriptor. If this case ever
* becomes real, a better solution may be to force-close a filp for
* /dev/tty when a new controlling terminal is opened.
*/
printf("VFS: file pointer has multiple controlling TTYs!\n");
return(EIO);
}
f->filp_char_select_dev = dev; /* set before possibly suspending */
rops = *ops;
/* By default, nothing to do */
*ops = 0;
if (!block && (f->filp_select_flags & FSF_BLOCKED)) {
/* This filp is blocked waiting for a reply, but we don't want to
* block ourselves. Unless we're awaiting the initial reply, these
* operations won't be ready */
if (!(f->filp_select_flags & FSF_BUSY)) {
if ((rops & SEL_RD) && (f->filp_select_flags & FSF_RD_BLOCK))
rops &= ~SEL_RD;
if ((rops & SEL_WR) && (f->filp_select_flags & FSF_WR_BLOCK))
rops &= ~SEL_WR;
if ((rops & SEL_ERR) && (f->filp_select_flags & FSF_ERR_BLOCK))
rops &= ~SEL_ERR;
if (!(rops & (SEL_RD|SEL_WR|SEL_ERR)))
return(OK);
}
}
f->filp_select_flags |= FSF_UPDATE;
if (block) {
rops |= SEL_NOTIFY;
if (rops & SEL_RD) f->filp_select_flags |= FSF_RD_BLOCK;
if (rops & SEL_WR) f->filp_select_flags |= FSF_WR_BLOCK;
if (rops & SEL_ERR) f->filp_select_flags |= FSF_ERR_BLOCK;
}
if (f->filp_select_flags & FSF_BUSY)
return(SUSPEND);
dp = &dmap[major(dev)];
if (dp->dmap_sel_busy)
return(SUSPEND);
f->filp_select_flags &= ~FSF_UPDATE;
r = cdev_select(dev, rops);
if (r != OK)
return(r);
dp->dmap_sel_busy = TRUE;
dp->dmap_sel_filp = f;
f->filp_select_flags |= FSF_BUSY;
return(SUSPEND);
}
/*===========================================================================*
* select_request_file *
*===========================================================================*/
static int select_request_file(struct filp *UNUSED(f), int *UNUSED(ops),
int UNUSED(block), struct fproc *UNUSED(rfp))
{
/* Files are always ready, so output *ops is input *ops */
return(OK);
}
/*===========================================================================*
* select_request_pipe *
*===========================================================================*/
static int select_request_pipe(struct filp *f, int *ops, int block,
struct fproc *UNUSED(rfp))
{
/* Check readiness status on a pipe. The given filp is locked. This function
* may block its calling thread if necessary.
*/
int orig_ops, r = 0, err;
orig_ops = *ops;
if ((*ops & (SEL_RD|SEL_ERR))) {
/* Check if we can read 1 byte */
err = pipe_check(f, READING, f->filp_flags & ~O_NONBLOCK, 1,
1 /* Check only */);
if (err != SUSPEND)
r |= SEL_RD;
if (err < 0 && err != SUSPEND)
r |= SEL_ERR;
}
if ((*ops & (SEL_WR|SEL_ERR))) {
/* Check if we can write 1 byte */
err = pipe_check(f, WRITING, f->filp_flags & ~O_NONBLOCK, 1,
1 /* Check only */);
if (err != SUSPEND)
r |= SEL_WR;
if (err < 0 && err != SUSPEND)
r |= SEL_ERR;
}
/* Some options we collected might not be requested. */
*ops = r & orig_ops;
if (!*ops && block)
f->filp_pipe_select_ops |= orig_ops;
return(OK);
}
/*===========================================================================*
* tab2ops *
*===========================================================================*/
static int tab2ops(int fd, struct selectentry *e)
{
int ops = 0;
if (FD_ISSET(fd, &e->readfds)) ops |= SEL_RD;
if (FD_ISSET(fd, &e->writefds)) ops |= SEL_WR;
if (FD_ISSET(fd, &e->errorfds)) ops |= SEL_ERR;
return(ops);
}
/*===========================================================================*
* ops2tab *
*===========================================================================*/
static void ops2tab(int ops, int fd, struct selectentry *e)
{
if ((ops & SEL_RD) && e->vir_readfds && FD_ISSET(fd, &e->readfds) &&
!FD_ISSET(fd, &e->ready_readfds)) {
FD_SET(fd, &e->ready_readfds);
e->nreadyfds++;
}
if ((ops & SEL_WR) && e->vir_writefds && FD_ISSET(fd, &e->writefds) &&
!FD_ISSET(fd, &e->ready_writefds)) {
FD_SET(fd, &e->ready_writefds);
e->nreadyfds++;
}
if ((ops & SEL_ERR) && e->vir_errorfds && FD_ISSET(fd, &e->errorfds) &&
!FD_ISSET(fd, &e->ready_errorfds)) {
FD_SET(fd, &e->ready_errorfds);
e->nreadyfds++;
}
}
/*===========================================================================*
* copy_fdsets *
*===========================================================================*/
static int copy_fdsets(struct selectentry *se, int nfds, int direction)
{
/* Copy FD sets from or to the user process calling select(2). This function
* MUST NOT block the calling thread.
*/
int r;
size_t fd_setsize;
endpoint_t src_e, dst_e;
fd_set *src_fds, *dst_fds;
if (nfds < 0 || nfds > OPEN_MAX)
panic("select copy_fdsets: nfds wrong: %d", nfds);
/* Only copy back as many bits as the user expects. */
fd_setsize = (size_t) (howmany(nfds, __NFDBITS) * sizeof(__fd_mask));
/* Set source and destination endpoints */
src_e = (direction == FROM_PROC) ? se->req_endpt : SELF;
dst_e = (direction == FROM_PROC) ? SELF : se->req_endpt;
/* read set */
src_fds = (direction == FROM_PROC) ? se->vir_readfds : &se->ready_readfds;
dst_fds = (direction == FROM_PROC) ? &se->readfds : se->vir_readfds;
if (se->vir_readfds) {
r = sys_datacopy_wrapper(src_e, (vir_bytes) src_fds, dst_e,
(vir_bytes) dst_fds, fd_setsize);
if (r != OK) return(r);
}
/* write set */
src_fds = (direction == FROM_PROC) ? se->vir_writefds : &se->ready_writefds;
dst_fds = (direction == FROM_PROC) ? &se->writefds : se->vir_writefds;
if (se->vir_writefds) {
r = sys_datacopy_wrapper(src_e, (vir_bytes) src_fds, dst_e,
(vir_bytes) dst_fds, fd_setsize);
if (r != OK) return(r);
}
/* error set */
src_fds = (direction == FROM_PROC) ? se->vir_errorfds : &se->ready_errorfds;
dst_fds = (direction == FROM_PROC) ? &se->errorfds : se->vir_errorfds;
if (se->vir_errorfds) {
r = sys_datacopy_wrapper(src_e, (vir_bytes) src_fds, dst_e,
(vir_bytes) dst_fds, fd_setsize);
if (r != OK) return(r);
}
return(OK);
}
/*===========================================================================*
* select_cancel_all *
*===========================================================================*/
static void select_cancel_all(struct selectentry *se)
{
/* Cancel select, possibly on success. Decrease select usage and cancel timer.
* This function MUST NOT block its calling thread.
*/
int fd;
struct filp *f;
for (fd = 0; fd < se->nfds; fd++) {
if ((f = se->filps[fd]) == NULL) continue;
se->filps[fd] = NULL;
select_cancel_filp(f);
}
if (se->expiry > 0) {
cancel_timer(&se->timer);
se->expiry = 0;
}
se->requestor = NULL;
}
/*===========================================================================*
* select_cancel_filp *
*===========================================================================*/
static void select_cancel_filp(struct filp *f)
{
/* Reduce the number of select users of this filp. This function MUST NOT block
* its calling thread.
*/
devmajor_t major;
assert(f);
assert(f->filp_selectors > 0);
assert(f->filp_count > 0);
f->filp_selectors--;
if (f->filp_selectors == 0) {
/* No one selecting on this filp anymore, forget about select state */
f->filp_select_ops = 0;
f->filp_select_flags = 0;
f->filp_pipe_select_ops = 0;
/* If this filp is the subject of an ongoing select query to a
* character device, mark the query as stale, so that this filp will
* not be checked when the result arrives. The filp select device may
* still be NO_DEV if do_select fails on the initial fd check.
*/
if (is_char_device(f) && f->filp_char_select_dev != NO_DEV) {
major = major(f->filp_char_select_dev);
if (dmap[major].dmap_sel_busy &&
dmap[major].dmap_sel_filp == f)
dmap[major].dmap_sel_filp = NULL; /* leave _busy set */
f->filp_char_select_dev = NO_DEV;
}
}
}
/*===========================================================================*
* select_return *
*===========================================================================*/
static void select_return(struct selectentry *se)
{
/* Return the results of a select call to the user process and revive the
* process. This function MUST NOT block its calling thread.
*/
int r;
assert(!is_deferred(se)); /* Not done yet, first wait for async reply */
select_cancel_all(se);
if (se->error != OK)
r = se->error;
else
r = copy_fdsets(se, se->nfds, TO_PROC);
if (r == OK)
r = se->nreadyfds;
revive(se->req_endpt, r);
}
/*===========================================================================*
* select_callback *
*===========================================================================*/
void select_callback(struct filp *f, int status)
{
/* The status of a filp has changed, with the given ready operations or error.
* This function is currently called only for pipes, and holds the lock to
* the filp.
*/
filp_status(f, status);
}
/*===========================================================================*
* init_select *
*===========================================================================*/
void init_select(void)
{
int s;
for (s = 0; s < MAXSELECTS; s++)
init_timer(&selecttab[s].timer);
}
/*===========================================================================*
* select_forget *
*===========================================================================*/
void select_forget(void)
{
/* The calling thread's associated process is expected to be unpaused, due to
* a signal that is supposed to interrupt the current system call. Totally
* forget about the select(). This function may block its calling thread if
* necessary (but it doesn't).
*/
int slot;
struct selectentry *se;
for (slot = 0; slot < MAXSELECTS; slot++) {
se = &selecttab[slot];
if (se->requestor == fp)
break;
}
if (slot >= MAXSELECTS) return; /* Entry not found */
assert(se->starting == FALSE);
/* Do NOT test on is_deferred here. We can safely cancel ongoing queries. */
select_cancel_all(se);
}
/*===========================================================================*
* select_timeout_check *
*===========================================================================*/
void select_timeout_check(minix_timer_t *timer)
{
/* An alarm has gone off for one of the select queries. This function MUST NOT
* block its calling thread.
*/
int s;
struct selectentry *se;
s = tmr_arg(timer)->ta_int;
if (s < 0 || s >= MAXSELECTS) return; /* Entry does not exist */
se = &selecttab[s];
if (se->requestor == NULL) return;
if (se->expiry <= 0) return; /* Strange, did we even ask for a timeout? */
se->expiry = 0;
if (!is_deferred(se))
select_return(se);
else
se->block = 0; /* timer triggered "too soon", treat as nonblocking */
}
/*===========================================================================*
* select_unsuspend_by_endpt *
*===========================================================================*/
void select_unsuspend_by_endpt(endpoint_t proc_e)
{
/* Revive blocked processes when a driver has disappeared */
devmajor_t major;
int fd, s;
struct selectentry *se;
struct filp *f;
for (s = 0; s < MAXSELECTS; s++) {
int wakehim = 0;
se = &selecttab[s];
if (se->requestor == NULL) continue;
if (se->requestor->fp_endpoint == proc_e) {
assert(se->requestor->fp_flags & FP_EXITING);
select_cancel_all(se);
continue;
}
for (fd = 0; fd < se->nfds; fd++) {
if ((f = se->filps[fd]) == NULL || !is_char_device(f))
continue;
assert(f->filp_char_select_dev != NO_DEV);
major = major(f->filp_char_select_dev);
if (dmap_driver_match(proc_e, major)) {
se->filps[fd] = NULL;
se->error = EIO;
select_cancel_filp(f);
wakehim = 1;
}
}
if (wakehim && !is_deferred(se))
select_return(se);
}
}
/*===========================================================================*
* select_reply1 *
*===========================================================================*/
void select_reply1(endpoint_t driver_e, devminor_t minor, int status)
{
/* Handle the initial reply to CDEV_SELECT request. This function MUST NOT
* block its calling thread.
*/
devmajor_t major;
dev_t dev;
struct filp *f;
struct dmap *dp;
/* Figure out which device is replying */
if ((dp = get_dmap(driver_e)) == NULL) return;
major = dp-dmap;
dev = makedev(major, minor);
/* Get filp belonging to character special file */
if (!dp->dmap_sel_busy) {
printf("VFS (%s:%d): major %d was not expecting a CDEV_SELECT reply\n",
__FILE__, __LINE__, major);
return;
}
/* The select filp may have been set to NULL if the requestor has been
* unpaused in the meantime. In that case, we ignore the result, but we do
* look for other filps to restart later.
*/
if ((f = dp->dmap_sel_filp) != NULL) {
/* Find vnode and check we got a reply from the device we expected */
assert(is_char_device(f));
assert(f->filp_char_select_dev != NO_DEV);
if (f->filp_char_select_dev != dev) {
/* This should never happen. The driver may be misbehaving.
* For now we assume that the reply we want will arrive later..
*/
printf("VFS (%s:%d): expected reply from dev %llx not %llx\n",
__FILE__, __LINE__, f->filp_char_select_dev, dev);
return;
}
}
/* No longer waiting for a reply from this device */
dp->dmap_sel_busy = FALSE;
dp->dmap_sel_filp = NULL;
/* Process the select result only if the filp is valid. */
if (f != NULL) {
assert(f->filp_count >= 1);
assert(f->filp_select_flags & FSF_BUSY);
f->filp_select_flags &= ~FSF_BUSY;
/* The select call is done now, except when
* - another process started a select on the same filp with possibly a
* different set of operations.
* - a process does a select on the same filp but using different file
* descriptors.
* - the select has a timeout. Upon receiving this reply the operations
* might not be ready yet, so we want to wait for that to ultimately
* happen.
* Therefore we need to keep remembering what the operations are.
*/
if (!(f->filp_select_flags & (FSF_UPDATE|FSF_BLOCKED)))
f->filp_select_ops = 0; /* done selecting */
else if (status > 0 && !(f->filp_select_flags & FSF_UPDATE))
/* there may be operations pending */
f->filp_select_ops &= ~status;
/* Record new filp status */
if (!(status == 0 && (f->filp_select_flags & FSF_BLOCKED))) {
if (status > 0) { /* operations ready */
if (status & SEL_RD)
f->filp_select_flags &= ~FSF_RD_BLOCK;
if (status & SEL_WR)
f->filp_select_flags &= ~FSF_WR_BLOCK;
if (status & SEL_ERR)
f->filp_select_flags &= ~FSF_ERR_BLOCK;
} else if (status < 0) { /* error */
/* Always unblock upon error */
f->filp_select_flags &= ~FSF_BLOCKED;
}
}
filp_status(f, status); /* Tell filp owners about the results */
}
select_restart_filps();
}
/*===========================================================================*
* select_reply2 *
*===========================================================================*/
void select_reply2(endpoint_t driver_e, devminor_t minor, int status)
{
/* Handle secondary reply to DEV_SELECT request. A secondary reply occurs when
* the select request is 'blocking' until an operation becomes ready. This
* function MUST NOT block its calling thread.
*/
int slot, found, fd;
devmajor_t major;
dev_t dev;
struct filp *f;
struct dmap *dp;
struct selectentry *se;
if (status == 0) {
printf("VFS (%s:%d): weird status (%d) to report\n",
__FILE__, __LINE__, status);
return;
}
/* Figure out which device is replying */
if ((dp = get_dmap(driver_e)) == NULL) {
printf("VFS (%s:%d): endpoint %d is not a known driver endpoint\n",
__FILE__, __LINE__, driver_e);
return;
}
major = dp-dmap;
dev = makedev(major, minor);
/* Find all file descriptors selecting for this device */
for (slot = 0; slot < MAXSELECTS; slot++) {
se = &selecttab[slot];
if (se->requestor == NULL) continue; /* empty slot */
found = FALSE;
for (fd = 0; fd < se->nfds; fd++) {
if ((f = se->filps[fd]) == NULL) continue;
if (!is_char_device(f)) continue;
assert(f->filp_char_select_dev != NO_DEV);
if (f->filp_char_select_dev != dev) continue;
if (status > 0) { /* Operations ready */
/* Clear the replied bits from the request
* mask unless FSF_UPDATE is set.
*/
if (!(f->filp_select_flags & FSF_UPDATE))
f->filp_select_ops &= ~status;
if (status & SEL_RD)
f->filp_select_flags &= ~FSF_RD_BLOCK;
if (status & SEL_WR)
f->filp_select_flags &= ~FSF_WR_BLOCK;
if (status & SEL_ERR)
f->filp_select_flags &= ~FSF_ERR_BLOCK;
ops2tab(status, fd, se);
} else {
f->filp_select_flags &= ~FSF_BLOCKED;
se->error = status;
}
found = TRUE;
}
/* Even if 'found' is set now, nothing may have changed for this call,
* as it may not have been interested in the operations that were
* reported as ready. Let restart_proc check.
*/
if (found)
restart_proc(se);
}
select_restart_filps();
}
/*===========================================================================*
* select_restart_filps *
*===========================================================================*/
static void select_restart_filps(void)
{
/* We got a result from a character driver, and now we need to check if we can
* restart deferred polling operations. This function MUST NOT block its
* calling thread.
*/
int fd, slot;
struct filp *f;
struct selectentry *se;
/* Locate filps that can be restarted */
for (slot = 0; slot < MAXSELECTS; slot++) {
se = &selecttab[slot];
if (se->requestor == NULL) continue; /* empty slot */
/* Only 'deferred' processes are eligible to restart */
if (!is_deferred(se)) continue;
/* Find filps that are not waiting for a reply, but have an updated
* status (i.e., another select on the same filp with possibly a
* different set of operations is to be done), and thus requires the
* select request to be sent again).
*/
for (fd = 0; fd < se->nfds; fd++) {
int r, wantops, ops;
if ((f = se->filps[fd]) == NULL) continue;
if (f->filp_select_flags & FSF_BUSY) /* Still waiting for */
continue; /* initial reply */
if (!(f->filp_select_flags & FSF_UPDATE)) /* Must be in */
continue; /* 'update' state */
/* This function is suitable only for character devices. In
* particular, checking pipes the same way would introduce a
* serious locking problem.
*/
assert(is_char_device(f));
wantops = ops = f->filp_select_ops;
r = select_request_char(f, &wantops, se->block, se->requestor);
if (r != OK && r != SUSPEND) {
se->error = r;
restart_proc(se);
break; /* Error or bogus return code; abort */
}
if (wantops & ops) ops2tab(wantops, fd, se);
}
}
}
/*===========================================================================*
* filp_status *
*===========================================================================*/
static void filp_status(f, status)
struct filp *f;
int status;
{
/* Tell processes that need to know about the status of this filp. This
* function MUST NOT block its calling thread.
*/
int fd, slot, found;
struct selectentry *se;
for (slot = 0; slot < MAXSELECTS; slot++) {
se = &selecttab[slot];
if (se->requestor == NULL) continue; /* empty slot */
found = FALSE;
for (fd = 0; fd < se->nfds; fd++) {
if (se->filps[fd] != f) continue;
if (status < 0)
se->error = status;
else
ops2tab(status, fd, se);
found = TRUE;
}
if (found)
restart_proc(se);
}
}
/*===========================================================================*
* restart_proc *
*===========================================================================*/
static void restart_proc(se)
struct selectentry *se;
{
/* Tell process about select results (if any) unless there are still results
* pending. This function MUST NOT block its calling thread.
*/
if ((se->nreadyfds > 0 || se->error != OK || !se->block) && !is_deferred(se))
select_return(se);
}
/*===========================================================================*
* wipe_select *
*===========================================================================*/
static void wipe_select(struct selectentry *se)
{
se->nfds = 0;
se->nreadyfds = 0;
se->error = OK;
se->block = 0;
memset(se->filps, 0, sizeof(se->filps));
FD_ZERO(&se->readfds);
FD_ZERO(&se->writefds);
FD_ZERO(&se->errorfds);
FD_ZERO(&se->ready_readfds);
FD_ZERO(&se->ready_writefds);
FD_ZERO(&se->ready_errorfds);
}
/*===========================================================================*
* select_lock_filp *
*===========================================================================*/
static void select_lock_filp(struct filp *f, int ops)
{
/* Lock a filp and vnode based on which operations are requested. This function
* may block its calling thread, obviously.
*/
tll_access_t locktype;
locktype = VNODE_READ; /* By default */
if (ops & (SEL_WR|SEL_ERR))
/* Selecting for error or writing requires exclusive access */
locktype = VNODE_WRITE;
lock_filp(f, locktype);
}
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