Fix up NFS client write error handling. Errors are split into recoverable and unrecoverable. For the former, we redirty the buffer and hang onto it for future retries. For the latter (eg. ESTALE), we discard the buffer and return the error back to the user on the next syscall. This fixes a number of vfs panics and fixes having a large number of dirty buffers (that cannot be written out and reclaimed) from hanging around. Thanks to ups@ for discussions on this issue.
Fix up NFS client write error handling. Errors are split into
recoverable and unrecoverable. For the former, we redirty the
buffer and hang onto it for future retries. For the latter (eg.
ESTALE), we discard the buffer and return the error back to the
user on the next syscall. This fixes a number of vfs panics and
fixes having a large number of dirty buffers (that cannot be
written out and reclaimed) from hanging around. Thanks to ups@
for discussions on this issue.

Reported by:	kris, Kai, others
Approved by:	re (kensmith)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase