Re: wasted open() on /etc/resolv.conf?

[Wil Cooley <wcooley@nakedape.cc>]

On Mon, Jan 29, 2001 at 08:13:14PM -0500, Michael B. Rash wrote:
> 
> Kernel 2.2.14-5.0:
> 
> Suppose that I put this following line in /etc/hosts:
>         216.32.74.52    www.yahoo.com
> ...and this line in /etc/nsswitch.conf
>         hosts:      files nisplus nis dns
> 
> Now, if I 'ping www.yahoo.com', my machine will not have to do an nslookup
> since the entry is in /etc/hosts, and doing 'tcpdump udp port 53' shows
> that no nslookup is performed if I do the ping.  Fine.
> 
> Now, if I run 'strace -e trace=open ping www.yahoo.com', I get the
> following in the output (among other things):
> 
> open("/etc/resolv.conf", O_RDONLY)      = 4
> open("/etc/nsswitch.conf", O_RDONLY)    = 4
> open("/etc/ld.so.cache", O_RDONLY)      = 4
> open("/etc/host.conf", O_RDONLY)        = 4
> open("/etc/hosts", O_RDONLY)            = 4
> 
> Since my machine does not need look up the address for www.yahoo.com, why
> is /etc/resolv.conf being opened at all?  There does not need to be any
> communication with the nameserver so doesn't this seem to be
> wasteful?
> 
> My only guess as to why this would happen might be that since most hosts
> will not be in /etc/hosts, it is a fairly safe assumption that
> nameservice will be needed for most communication so why not at least open
> the file anyway.  Anyone know if this is correct?
> 
> Can anyone point me to the appropriate kernel source files (I guess in
> the IP stack) to investigate this further?

No, this is actually a resolver issue, not kernel.  Try the glibc
source instead.

Wil
-- 
W. Reilly Cooley                         wcooley@nakedape.cc
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