[ moved from source-changes@ ]

> |    > Module Name:	src
> |    > Committed By:	christos
> |    > Date:		Sat Jul  1 15:38:28 UTC 2006
> |    > 
> |    > Modified Files:
> |    > 	src/sys/kern: uipc_socket2.c
> |    > 
> |    > Log Message:
> |    > Revert previous change to bump the socket low watermark to sock_loan_thresh.
> |    > With sock_loan_thresh=4096, sb_lowat==sb_hiwat, and sowritable will never
> |    > be true (even if only a single byte is pending). Some programs (like screen)
> |    > expect select() to return that a socket is writable on a socket when there
> |    > is space to write to it. XXX: What is the right thing to do here?
> |    
> |    i guess the right thing is fixing the configure script...
> | 
> | 
> | why is it wrong?
> 
> This is the script; it writes 4 bytes to the socket, and expects that
> the second select will return 2, one for the socket being readable,
> and one for being writable. The socket "sowritable" test will always
> fail if sb_hiwat == sb_lowat and there are bytes in the queue.
> 
> Another way to "fix" the problem is to increase the high watermark
> if not set to be lowat + MCLBYTES.
> 
> christos

why MCLBYTES?

i don't want to tweak kernel for a configure script.
is there any other application which is known to have a problem?

YAMAMOTO Takashi

> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> 
> char *nam = "/tmp/conftest20904";
> 
> main()
> {
>   fd_set f;
>   int rv = 0;
> 
>   (void)alarm(5);
>   unlink(nam);
>   if (mkfifo(nam, 0777))
>     exit(1);
>   close(0);
>   if (open(nam, O_RDWR | O_NONBLOCK))
>     exit(1);
>   if (write(0, "TEST", 4) == -1)
>     exit(1);
> 
>   FD_SET(0, &f);
>   if (select(1, &f, 0, 0, 0) == -1)
>     rv = 1;
>   if (select(1, &f, &f, 0, 0) != 2)
>     rv = 1;
>   return 0;
> }