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DragonFly bugs List (threaded) for 2010-08
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select() hangs on EOF

From: Johannes Hofmann <johannes.hofmann@xxxxxx>
Date: 22 Aug 2010 20:55:10 GMT


lang/guile no longer works since the recent kevent changes.
The problem is that select() for read now hangs when a fd on a local
file has reached EOF.

The following test program shows the issue (touch foo.txt before

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/select.h>
#include <sys/types.h>

main ()
    int result, fd;
    fd_set rset;

    if ((fd = open("foo.txt", O_RDONLY)) < 0) {
        printf ("Error %d opening foo.txt\n", errno);
        exit (-1);

    lseek(fd, 0, SEEK_END);

    FD_ZERO (&rset);
    FD_SET (fd, &rset);

    result = select (fd + 1, &rset, 0, 0, 0);
    printf("select returned %d\n", result);

The following change makes guile work (on hammer), but I don't know
whether this is the right place to deal with this.

diff --git a/sys/vfs/hammer/hammer_vnops.c b/sys/vfs/hammer/hammer_vnops.c
index d02b004..7b000a1 100644
--- a/sys/vfs/hammer/hammer_vnops.c
+++ b/sys/vfs/hammer/hammer_vnops.c
@@ -3413,7 +3413,7 @@ filt_hammerread(struct knote *kn, long hint)
 	kn->kn_data = ip->ino_data.size - kn->kn_fp->f_offset;
-	return (kn->kn_data != 0);
+	return (1);
 static int


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