From: Giacomo Tesio <giacomo@tesio.it>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: [9fans] read9pmsg usage
Date: Mon, 10 Aug 2015 16:11:19 +0200 [thread overview]
Message-ID: <CAHL7psFD9_xWyfPTbh0tCY80=KfRUzfkh5rm_Fij8WJzw2NmJg@mail.gmail.com> (raw)
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Hi, I've a probably naive question that I can't figure out.
I've just noticed that fcall(2) states
> Read9pmsg calls read(2) multiple times, if necessary, to
> read an entire 9P message into buf. The return value is 0
> for end of file, or -1 for error; it does not return partial
> messages.
>
>
but I've noticed that a few client does not interpret a 0 return value as a
EOF, eg
https://github.com/brho/plan9/blob/master/sys/src/cmd/usb/lib/fs.c#L604-L606
https://github.com/brho/plan9/blob/master/sys/src/cmd/usb/audio/audiofs.c#L889-L891
https://github.com/brho/plan9/blob/master/sys/src/cmd/aux/searchfs.c#L613-L615
https://github.com/brho/plan9/blob/master/sys/src/cmd/lnfs.c#L547-L551
https://github.com/brho/plan9/blob/master/sys/src/cmd/telco/telco.c#L935-L937
The comment there states that
/*
* reading from a pipe or a network device
* will give an error after a few eof reads.
* however, we cannot tell the difference
* between a zero-length read and an interrupt
* on the processes writing to us,
* so we wait for the error.
*/
However many other fs just handle errors and eof together, for example here:
https://github.com/brho/plan9/blob/master/sys/src/cmd/ip/ftpfs/ftpfs.c#L273-L279
I'm a bit confused about this. What's the proper use of the 0 return value?
Giacomo
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next reply other threads:[~2015-08-10 14:11 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-10 14:11 Giacomo Tesio [this message]
2015-08-10 14:22 ` erik quanstrom
2015-08-10 14:35 ` Giacomo Tesio
2015-08-10 14:54 ` Charles Forsyth
2015-08-10 15:40 ` Charles Forsyth
2015-08-10 20:17 ` Giacomo Tesio
2015-08-10 20:33 ` Charles Forsyth
2015-08-11 15:48 ` Charles Forsyth
2015-08-12 0:21 ` Giacomo Tesio
2015-08-12 7:25 ` David du Colombier
2015-08-12 9:18 ` Giacomo Tesio
2015-08-12 17:17 ` Charles Forsyth
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