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/* fd.c -- file descriptor manipulations ($Revision: 1.2 $) */
#include "es.h"
/* mvfd -- duplicate a fd and close the old */
extern void mvfd(int old, int new) {
if (old != new) {
int fd = dup2(old, new);
if (fd == -1)
fail("es:mvfd", "dup2: %s", esstrerror(errno));
assert(fd == new);
close(old);
}
}
/*
* deferred file descriptor operations
* we maintain a stack of file descriptor operations as they occur,
* if we're operating in the context of a parent shell. (if we're
* already in a forked process, we just do them.) the operations
* are actually done at closefds() time.
*/
typedef struct {
int realfd, userfd;
} Defer;
static Defer *deftab;
static int defcount = 0, defmax = 0;
static void dodeferred(int realfd, int userfd) {
assert(userfd >= 0);
releasefd(userfd);
if (realfd == -1)
close(userfd);
else {
assert(realfd >= 0);
mvfd(realfd, userfd);
}
}
static int pushdefer(Boolean parent, int realfd, int userfd) {
if (parent) {
Defer *defer;
if (defcount >= defmax) {
int i;
for (i = 0; i < defcount; i++)
unregisterfd(&deftab[i].realfd);
defmax += 10;
deftab = erealloc(deftab, defmax * sizeof (Defer));
for (i = 0; i < defcount; i++)
registerfd(&deftab[i].realfd, TRUE);
}
defer = &deftab[defcount++];
defer->realfd = realfd;
defer->userfd = userfd;
registerfd(&defer->realfd, TRUE);
return defcount - 1;
} else {
dodeferred(realfd, userfd);
return UNREGISTERED;
}
}
extern int defer_mvfd(Boolean parent, int old, int new) {
assert(old >= 0);
assert(new >= 0);
return pushdefer(parent, old, new);
}
extern int defer_close(Boolean parent, int fd) {
assert(fd >= 0);
return pushdefer(parent, -1, fd);
}
extern void undefer(int ticket) {
if (ticket != UNREGISTERED) {
Defer *defer;
assert(ticket >= 0);
assert(defcount > 0);
defer = &deftab[--defcount];
assert(ticket == defcount);
unregisterfd(&defer->realfd);
if (defer->realfd != -1)
close(defer->realfd);
}
}
/* fdmap -- turn a deferred (user) fd into a real fd */
extern int fdmap(int fd) {
int i = defcount;
while (--i >= 0) {
Defer *defer = &deftab[i];
if (fd == defer->userfd) {
fd = defer->realfd;
if (fd == -1)
return -1;
}
}
return fd;
}
/* remapfds -- apply the fd map to the current file descriptor table */
static void remapfds(void) {
Defer *defer, *defend = &deftab[defcount];
for (defer = deftab; defer < defend; defer++) {
unregisterfd(&defer->realfd);
dodeferred(defer->realfd, defer->userfd);
}
defcount = 0;
}
/*
* the registered file descriptor list
* this is actually a list of pointers to file descriptors.
* when we start to work with a user-defined fd, we scan
* this list (releasefds) and it an entry matches the user
* defined one, we dup it to a different number. when we fork,
* we close all the descriptors on this list.
*/
typedef struct {
int *fdp;
Boolean closeonfork;
} Reserve;
static Reserve *reserved = NULL;
static int rescount = 0, resmax = 0;
/* registerfd -- reserve a file descriptor for es */
extern void registerfd(int *fdp, Boolean closeonfork) {
#if ASSERTIONS
int i;
for (i = 0; i < rescount; i++)
assert(fdp != reserved[i].fdp);
#endif
if (rescount >= resmax) {
resmax += 10;
reserved = erealloc(reserved, resmax * sizeof (Reserve));
}
reserved[rescount].fdp = fdp;
reserved[rescount].closeonfork = closeonfork;
rescount++;
}
/* unregisterfd -- give up our hold on a file descriptor */
extern void unregisterfd(int *fdp) {
int i;
assert(reserved != NULL);
assert(rescount > 0);
for (i = 0; i < rescount; i++)
if (reserved[i].fdp == fdp) {
reserved[i] = reserved[--rescount];
return;
}
panic("%x not on file descriptor reserved list", fdp);
}
/* closefds -- close file descriptors after a fork() */
extern void closefds(void) {
int i;
remapfds();
for (i = 0; i < rescount; i++) {
Reserve *r = &reserved[i];
if (r->closeonfork) {
int fd = *r->fdp;
if (fd >= 3)
close(fd);
*r->fdp = -1;
}
}
}
/* releasefd -- release a specific file descriptor from its es uses */
extern void releasefd(int n) {
int i;
assert(n >= 0);
for (i = 0; i < rescount; i++) {
int *fdp = reserved[i].fdp;
int fd = *fdp;
if (fd == n) {
*fdp = dup(fd);
if (*fdp == -1) {
assert(errno != EBADF);
fail("es:releasefd", "%s", esstrerror(errno));
}
close(fd);
}
}
}
/* isdeferred -- is this file descriptor on the deferral list */
static Boolean isdeferred(int fd) {
Defer *defer, *defend = &deftab[defcount];
for (defer = deftab; defer < defend; defer++)
if (defer->userfd == fd)
return TRUE;
return FALSE;
}
/* newfd -- return a new, free file descriptor */
extern int newfd(void) {
int i;
for (i = 3;; i++)
if (!isdeferred(i)) {
int fd = dup(i);
if (fd == -1) {
if (errno != EBADF)
fail("$&newfd", "newfd: %s", esstrerror(errno));
return i;
} else if (isdeferred(fd)) {
int n = newfd();
close(fd);
return n;
} else {
close(fd);
return fd;
}
}
}
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