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From: rob@ptsfb.UUCP (Rob Bernardo)
Newsgroups: net.unix-wizards
Subject: Re: a question on open() and lseek()
Message-ID: <352@ptsfb.UUCP>
Date: Tue, 15-Apr-86 09:42:39 EST
Article-I.D.: ptsfb.352
Posted: Tue Apr 15 09:42:39 1986
Date-Received: Fri, 18-Apr-86 04:05:59 EST
References: <2594@brl-smoke.ARPA>
Reply-To: rob@ptsfb.UUCP (Rob Bernardo)
Organization: Pacific Bell, San Francisco
Lines: 23

In article <2594@brl-smoke.ARPA> moi%brandeis.csnet@csnet-relay.arpa writes:
>
>	The manual page for "open()" mentions that one of the flags one
>	can specify with the call is O_APPEND.  It's supposed to request
>	that all "write()"s be appended to the end of the file.  Is
>	there any reason to use the sequence:
>		f = open( file, O_WRONLY );
>		lseek( f, 0, L_XTND );
>	instead of the single call:
>		f = open( file, O_WRONLY | O_APPEND );

None that I can think of. You would have to so the lseek() call before every
write() if there might be another process appending to the same file.
And that could fail because between your lseek() and your write()
your process might get swapped out and the other appending process might write
at the end of the file; your write() would then overwrite that of the other
process, rather than be at the end of the file. I've seen this happen
where there was a common error log file for a set of related
programs on a system where the O_APPEND flag was broken causing the implicit
lseek to take place only after the open, but no before each write.

Rob Bernardo, San Ramon, CA    (415) 823-2417    {ihnp4|dual|qantel}!ptsfa!rob
			       Pacific * Bell