bug#29038: df hangs on fifos/named pipes

[Paul Eggert]

Pádraig Brady wrote:

> I suppose we could stat() and if that succeeds && !fifo, only then call open() ?
> Patch to do that is attached.

Better is to use open with O_NONBLOCK, as this avoids interpreting the file name 
twice in the usual case. Better yet is to use O_PATH if available, as this 
avoids interpreting the file name twice even when the file is unreadable or is a 
FIFO that would block. Also, the comment just before the code should be changed 
to match the altered code. Proposed followup patch attached.

It is puzzling that df calls fstat or stat, when it should just be calling 
fstatfs or statfs. But that is a different matter.

0001-df-improve-fix-for-FIFOs.patch
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