CVS commit: syssrc

[Jason R Thorpe <thorpej%netbsd.org@localhost>]

Module Name:    syssrc
Committed By:   thorpej
Date:           Thu Jun  7 01:29:17 UTC 2001

Modified Files:
        syssrc/sys/kern: kern_descrip.c uipc_usrreq.c
        syssrc/sys/sys: filedesc.h

Log Message:
Rework fdalloc() even further: split fdalloc() into fdalloc() and
fdexpand().  The former will return ENOSPC if there is not space
in the current filedesc table.  The latter performs the expansion
of the filedesc table.  This means that fdalloc() won't ever block,
and it gives callers an opportunity to clean up before the
potentially-blocking fdexpand() call.

Update all fdalloc() callers to deal with the need-to-fdexpand() case.

Rewrite unp_externalize() to use fdalloc() and fdexpand() in a
safe way, using an algorithm suggested by Bill Sommerfeld:
- Use a temporary array of integers to hold the new filedesc table
  indexes.  This allows us to repeat the loop if necessary.
- Loop through the array of file *'s, assigning them to filedesc table
  slots.  If fdalloc() indicates expansion is necessary, undo the
  assignments we've done so far, expand, and retry the whole process.
- Once all file *'s have been assigned to slots, update the f_msgcount
  and unp_rights counters.
- Right before we return, copy the temporary integer array to the message
  buffer, and trim the length as before.
Note that once locking is added to the filedesc array, this entire
operation will be `atomic', in that the lock will be held while
file *'s are assigned to embryonic table slots, thus preventing anything
else from using them.


To generate a diff of this commit:
cvs rdiff -r1.75 -r1.76 syssrc/sys/kern/kern_descrip.c
cvs rdiff -r1.49 -r1.50 syssrc/sys/kern/uipc_usrreq.c
cvs rdiff -r1.21 -r1.22 syssrc/sys/sys/filedesc.h

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.