Not very much about Solaris NFS filehandles
A lot of Unix systems have NFS filehandles that are easy to recognize and decipher, at least to the extent of easily mapping filehandles to the server's filesystems (such information is very useful for things like troubleshooting just which server filesystem is seeing lots of NFS traffic from one particular client). Solaris does not.
The basic structure of a Solaris NFS v3 filehandle is as follows, at least as of Solaris 10 U8 or so:
|4||overall filehandle length in XDR byte order|
(The overall filehandle is rounded up to be a multiple of 4 bytes long.)
All fields except the overall filehandle length are in host byte order, not network byte order. If you do not know the byte order of the Solaris fileserver you're working with, you already have problems.
(By the way, this implies that you cannot possibly do transparent failover between Solaris fileservers of different CPU architectures.)
The most interesting field is
fh3_fsid, which identifies the server
filesystem. I could talk about the inner structure of this, but at least
for ZFS the practical answer is that you don't care; you need to directly
extract the fsid from the NFS code with
mdb and some parsing.
The raw fsid is printed by
::nfs_exptable as part of dumping the
entire NFS export table and information:
echo ::nfs_exptable | mdb -k
With suitable parsing this will directly give you the
for every NFS-exported filesystem. On S10U8, the fsid is reported
fsid: (0x9d7c697f 0xbeb5c208)
Other versions of Solaris have reported this in somewhat different formats. Expect to spend a certain amount of effort to maintain your parser as new versions of Solaris have new mdb output.
The inner life of the fsid
The low byte of
fh3_fsid contains an identifier of
the filesystem type; the remaining bits are filesystem type specific.
For ZFS they are a 56-bit objset unique ID, with the low 32 bits in
fh3_fsid and the remaining bits in the high three bytes of
My skill at understanding Solaris kernel source is insufficient to establish if the filesystem type identifier is constant, and if so how constant it is. (Is it fixed permanently for ZFS, fixed per OS release, fixed per machine but variable from one machine to another, or variable if the system configuration changes? I can't understand the source environment enough to tell.)
As it happens it doesn't matter, because for ZFS there is basically no simple way of finding out the 56-bit objset unique ID; as far as I can tell there is simply no interface or even readily accessible data structure where it is visible.
Comments on this page:Written on 27 January 2011.