[TUHS] fstat(2) on pipes?

Clem Cole clemc at ccc.com
Tue Aug 16 03:53:28 AEST 2016

​Yet Another Example of UNIX A != UNIX B​

IIRC from the /usr/group and later POSIX discussions, the only thing that
is for sure on the stat structure with a PIPE is that it's marked as such.

That said, I just grabbed my copy of the SVID (Vol 1 pages 126-127)

st_size "For ordinary files, this field is the address of the end of file.
  For pipes and FIFO's, this field is the count of the data currently in
the file.   For block-special & char special, this field is undefined."

As for st_ino and st_dev -- the SVID says the ino "uniquely identifies the
file in a given file system," and dev uniquely identifies the file system
that contains the file."

It further states: "The pair of fields st_ino and st_dev uniquely
identifies ordinary files."     And then later says "No other significance
is associated with this value."

So..... clearly returning an error is wrong.   I don't think the Linux
scheme hurts anything....

On Sun, Aug 14, 2016 at 8:11 PM, Warren Toomey <wkt at tuhs.org> wrote:

> All, sorry this is slightly off-topic. I'm trying to
> find out what fstat(2) returns when the file descriptor
> is a pipe. The POSIX/Open Group documentation doesn't
> really specify what should be returned. Does anybody have
> any pointers?
> Thanks, Warren
> P.S. Why? xv6 has fstat() but returns an error if the
> file descriptor isn't associated with an i-node. I'm
> trying to work out if/how to fix it.
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