Bug 7932

this looks correct to me. Did  any process have the pipe open for writting? If
not, returning 0 is the right thing to do, as the paragraph you quoted states.

Please send complete small testcase and repoen if disagree.

The pipe in the listed code fragment *is* open for writing; it's in p[1],
the write-side of the pipe (it was never closed).  I have included below a
more detailed test-case that proves the point of the original defect filed.

Note that when compiled "as is" *and* when compiled -DREAD_ONLY (to close the
write-side of the pipe before calling scanf()), BOTH cases result in errno
29 (ESPIPE == Illegal seek) from the scanf() call.  This return is acceptable
if the write-side is closed but POSIX clearly states that when the write-side
is open, errno EAGAIN is to be returned when there's (a) no data available
and (b) O_NONBLOCK is set.

Newer test code follows -- let me know if you have any questions.  (Glen)
[snip]
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>

#define STRING  "This is a string"

main()
{
        int flags, val, p[2], len = strlen(STRING);
        FILE *fp;
        char inbuf[64];

        if (pipe(p) < 0) {
                perror("pipe");
                exit(1);
        }
        if ((flags = fcntl(p[0], F_GETFL)) < 0) {
                perror("fcntl(F_GETFL)");
                exit(1);
        }
        if (fcntl(p[0], F_SETFL, flags | O_NONBLOCK) < 0) {
                perror("fcntl(F_SETFL)");
                exit(1);
        }
        if ((fp = fdopen(p[0], "r")) == (FILE *) NULL) {
                perror("fdopen");
                exit(1);
        }
#ifdef  READ_ONLY
        printf("DEBUG: Closing write-side of pipe...\n");
        if (close(p[1]) < 0) {
                perror("close");
                exit(1);
        }
#endif  /* READ_ONLY */
#ifdef  FORCE_FEED
        printf("DEBUG: Forcing data into pipe: \"%s\"\n", STRING);
        if (write(p[1], STRING, len) != len) {
                perror("write");
                exit(1);
        }
#elif   DEBUG_READ
        printf("DEBUG: calling read() instead of fscanf()\n");
        if (read(p[0], inbuf, BUFSIZ) < 0) {
                perror("read");
                if (errno == EAGAIN) {
                        printf("Proper return failure from read()\n");
                        exit(0);
                }
        }
        exit(1);
#endif  /* DEBUG_READ */
        if ((val = fscanf(fp, "%s", inbuf)) == EOF) {
                if (errno != EAGAIN) {
                        perror("fscanf");
                        exit(1);
                }
                printf("errno = EAGAIN (%d), correct ala POSIX\n", errno);
                exit(0);
        }
        fprintf(stderr, "fscanf() returns %d\n", val);
        fprintf(stderr, "fscanf() found data: \"%s\"\n", inbuf);
#ifdef  FORCE_FEED
        exit(0);
#endif  /* FORCE_FEED */
        exit(1);
}

reprioritize

assign to jakub