Advanced Programming in the UNIX® Environment

ptg10805159

698 Te rminal I/O Chapter 18

strcmp(pathname, "/dev/stdout") == 0 ||

strcmp(pathname, "/dev/stderr") == 0)

continue;

if (stat(pathname, &devstat) < 0)

continue;

if (S_ISDIR(devstat.st_mode)) {

add(pathname);

continue;

}

if (devstat.st_ino == fdstatp->st_ino &&

devstat.st_dev == fdstatp->st_dev) { /* found a match */

closedir(dp);

return(pathname);

}

}

closedir(dp);

return(NULL);

}

char *

ttyname(int fd)

{

struct stat fdstat;

struct devdir *ddp;

char *rval;

if (isatty(fd) == 0)

return(NULL);

if (fstat(fd, &fdstat) < 0)

return(NULL);

if (S_ISCHR(fdstat.st_mode) == 0)

return(NULL);

rval = searchdir("/dev", &fdstat);

if (rval == NULL) {

for (ddp = head; ddp != NULL; ddp = ddp->d_next)

if ((rval = searchdir(ddp->d_name, &fdstat)) != NULL)

break;

}

cleanup();

return(rval);

}

Figure 18.15Implementation of POSIX.1ttynamefunction

The technique is to read the/devdirectory,looking for an entry with the same

device number and i-node number.Recall from Section 4.24 that each file system has a

unique device number (thest_devfield in thestatstructure, from Section 4.2), and

each directory entry in that file system has a unique i-node number (thest_inofield in

thestatstructure). Weassume in this function that when we hit a matching device