// Return the 'struct Fd' for a file descriptor number.
// Returns NULL on failure, a pointer on success.
// If 'must_exist' is true, then the file descriptor must currently be open
// or NULL is returned.
// Returns 0 on success, < 0 error code on failure.
//
int
fd_lookup(int fdnum, struct Fd **fd_store, bool must_exist)
{
struct Fd *fd = (struct Fd *) (FDTABLE + fdnum * PGSIZE);
if (fdnum < 0 || fdnum >= NFD || (must_exist && !fd_isopen(fd))) {
*fd_store = 0;
return -E_INVAL;
} else {
*fd_store = fd;
return 0;
}
}
// Finds the smallest index from 0 to NFD-1 that doesn't have
// its fd page mapped.
// Sets *fd_store to the corresponding fd page virtual address.
//
// Does NOT actually allocate an fd page.
// It is up to the caller to allocate the page somehow.
// This means that if someone calls fd_find_unused twice in a row
// without allocating the first page we return, we'll return the same
// page the second time.
//
// Returns 0 on success, < 0 on error. Errors are:
// -E_MAX_FD: no more file descriptors
// On error, *fd_store is set to 0.
int
fd_find_unused(struct Fd **fd_store)
{
int i;
struct Fd *fd;
for (i = 0; i < NFD; i++) {
(void) fd_lookup(i, &fd, false);
if (!fd_isopen(fd)) {
*fd_store = fd;
return 0;
}
}
*fd_store = 0;
return -E_MAX_OPEN;
}
/*
* NAME
* fd2 - redirect from/to file descriptor 2
*
* SYNOPSIS
* fd2 [-e] [-f file] [--] command [arg ...]
*
* DESCRIPTION
* See the fd2(1) manual page for full details.
*/
int
main(int argc, char **argv)
{
bool eopt;
int efd, fd, nfd, ofd, opt;
char *file;
setmyerrexit(&ut_errexit);
setmyname(argv[0]);
setmypid(getpid());
/*
* Set-ID execution is not supported.
*/
if (geteuid() != getuid() || getegid() != getgid())
err(FC_ERR, FMT2S, getmyname(), ERR_SETID);
/*
* File descriptors 0, 1, and 2 must be open.
*/
for (fd = 0; fd < 3; fd++)
if (!fd_isopen(fd))
err(FC_ERR, "%s: %u: %s\n",
getmyname(), (unsigned)fd, strerror(errno));
ofd = FD1, efd = FD2;
eopt = false, file = NULL;
while ((opt = getopt(argc, argv, ":ef:")) != -1)
switch (opt) {
case 'e':
eopt = true;
break;
case 'f':
file = optarg;
break;
default:
usage();
}
argc -= optind;
argv += optind;
if (argc < 1)
usage();
if (file != NULL) {
if ((nfd = open(file, O_WRONLY|O_APPEND|O_CREAT, 0666)) == -1)
err(FC_ERR, FMT3S, getmyname(), file, ERR_CREATE);
if (dup2(nfd, efd) == -1)
err(FC_ERR, FMT2S, getmyname(), strerror(errno));
if (eopt && dup2(efd, ofd) == -1)
err(FC_ERR, FMT2S, getmyname(), strerror(errno));
(void)close(nfd);
} else {
if (eopt)
ofd = FD2, efd = FD1;
if (dup2(ofd, efd) == -1)
err(FC_ERR, FMT2S, getmyname(), strerror(errno));
}
/*
* Try to execute the specified command.
*/
(void)err_pexec(argv[0], argv);
/*NOTREACHED*/
return FC_ERR;
}
