read() called twice for /proc files

From: Tim Hockin (
Date: Mon Sep 24 2001 - 20:34:14 EST

woops! sent too early!

Is there a general solution to the case of read() being called minimum
twice for a file in /proc? I have a small file in /proc, whose data takes
a fair time to generate. My read() handler gets called once for the data,
and once so I can return 0 to terminate read().

This results in the actual read taking twice as long. Perhaps I am missing

What if the proc generic stuff used file->private_data as an EOF flag. It
seems really bizarre that the read loop loops until return 0 or eof is
set. We promptly throw away the EOF information that the read() handler

Would it break anything? Is there something I am not seeing in the larger

Tim Hockin
Systems Software Engineer
Sun Microsystems, Cobalt Server Appliances
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