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Re: [Xen-devel] Re: [Xen-changelog] Make xenstored reopen its trace file

To: Hollis Blanchard <hollisb@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [Xen-changelog] Make xenstored reopen its trace file on SIGHUP. This allows one to rotate the
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Mon, 07 Nov 2005 11:36:53 -0600
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Ewan Mellor <ewan@xxxxxxxxxxxxx>
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Hollis Blanchard wrote:

On Monday 07 November 2005 11:15, Anthony Liguori wrote:
perror and strlen are not safe to call from a signal handler.

I suggest just removing the perror call altogether and replacing strlen
with sizeof() - 1.

I'm really not sure how strlen could be non-threadsafe. I don't care if it's not in your list; your list doesn't include strtok_r either, and that is explicitly thread-safe. :-P
So re-reading the manpage, the list of safe functions is a POSIX-ism. That's perhaps why the thread-safe string functions aren't there since those are defined by ANSI not POSIX.

Regards,

Anthony Liguori

However, in addition to perror, another thread could try to use tracefd between the close and the open. You'd probably want to do something like:
        oldfd = tracefd;
        newfd = open();
        if (newfd < 0) {
                ...
        }
        tracefd = newfd;
        close(oldfd);

Finally, you really should do error-checking on close(). See the close(2) man page...



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