Subject: Determining if a file is on a local or r
To: 'SMTP:email@example.com' <tech-kern@NetBSD.ORG>
From: SYD) <Brian_de_Alwis@oti.com (Brian de Alwis>
Date: 07/16/1997 01:36:37
Not strictly a NetBSD question, but it will apply.
We want to be able to determine whether a file is on a local or remote (NFS)
system. Each Unix variant does it differently, and the only sure way seems
to find the filesystem mount-point and then grovel through the mounted
filesystems and check it's fstype.
But there does seem to be an easier way using stat(2)'s st_dev field.
According to the Solaris documentation, st_dev should be NODEV (=
(dev_t)(-1)) on a remote filesystem. AIX seems to agree. The only problem is
that this isn't true.
But what does seem to be consistent is that if st_dev is treated as a signed
number, then it will be a negative number for remote filesystems (the
highest bit is set). This holds on Solaris, AIX, HPUX... But I don't have
any other systems here to test it on.
I don't know where to look for any sort of confirmation. Is it a fluke, or
is it undocumented behaviour? What does the BSD4.3 and 4.4 implementation
say? Is it 'accepted practice'? What do other Unix variants do?
I'd be grateful for any help.