Date: Mon, 6 Apr 1998 21:30:01 -0700 (PDT) From: Matthew Dillon <dillon@backplane.com> To: freebsd-bugs Subject: Re: kern/6212: Two bugs with MFS filesystem fixed, two features added Message-ID: <199804070430.VAA16080@hub.freebsd.org>
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The following reply was made to PR kern/6212; it has been noted by GNATS.
From: Matthew Dillon <dillon@backplane.com>
To: freebsd-gnats-submit@freebsd.org
Cc: Subject: Re: kern/6212: Two bugs with MFS filesystem fixed, two features added
Date: Mon, 6 Apr 1998 21:22:21 -0700 (PDT)
This is a revised submission to my original submission. Note that the
diff included below is relative to the CVS base, *NOT* to my original
submission.
This submission fixes two bugs with MFS and adds two features that allow
MFS to be used properly in a diskless workstation environment.
Bug #1 fixed: kernel does not set P_SYSTEM flag for MFS special
kernel process, causing paging system to attempt to
kill the MFS process if memory runs low.
Bug #2 fixed: When using file-backed storage, the dirty pages are
never synchronized to the backing store by the
kernel update/syncer daemon. The MFS special kernel
process must call msync(). The fix causes it to call
msync() every 30 seconds.
Feature #1 added: MFS does not attempt to zero-out the file before
newfs'ing it if the file is already the correct
size. This allows MFS to be used with NFS-mounted
backing store without eating the network alive.
(e.g. my workstation has two 32MB MFS mounts and
one 8MB mount. That hurts on a 10BaseT network
without this fix).
Feature #2 added: The ability to specify file-backed storage and have
MFS *NOT* newfs the storage, allowing persistent
backing store to survive a reboot.
This is critical in a workstation environment because
it allows MFS to be used over an NFS-based file backing
store in a persistant fashion (i.e. for a small /home
so one can use SSH and .Xauthority in a diskless
workstation environment).
Note that fsck works just fine on the backing store
file.
Finally, it should be noted that being able to use an NFS-based file
for backing store for an MFS filesystem is critical in a diskless
workstation environment. It allows the filesystems in question to not
eat up memory, especially if the workstation environment has no swap
at all.
I would also like to submit instructions to the FreeBSD manual to
describe how to setup a diskless (floppy boot) workstation environment.
It really is quite simple.. a read-only NFS mount for / and /usr, a
secure r+w NFS mount for the MFS filesystem images, and three MFS
filesytems (two transitory: /var and /var/tmp, and one persistent: /home).
It's a fantastic environment, and MFS is extremely stable where as trying
to use vnconfig with an NFS-backed file leads to massive system corruption
and crashes even under FreeBSD-3.0-current. Since MFS disassociates I/O
with a separate kernel process, it can deal with NFS based backing store
without screwing up the machine.
-Matt
Matthew Dillon Engineering, BEST Internet Communications, Inc.
<dillon@backplane.com>
[always include a portion of the original email in any response!]
Index: mkfs.c
===================================================================
RCS file: /src/FreeBSD-CVS/ncvs/src/sbin/newfs/mkfs.c,v
retrieving revision 1.21
diff -r1.21 mkfs.c
42a43
> #include <sys/stat.h>
108a110
> extern int skipnewfs;
181c183,185
< fd = open(filename,O_RDWR|O_TRUNC|O_CREAT,0644);
---
> struct stat st;
>
> fd = open(filename,O_RDWR|O_CREAT,0644);
186,191c190,193
< for(l=0;l< fssize * sectorsize;l += l1) {
< l1 = fssize * sectorsize;
< if (BUFSIZ < l1)
< l1 = BUFSIZ;
< if (l1 != write(fd,buf,l1)) {
< perror(filename);
---
> fstat(fd, &st);
> if (st.st_size != fssize * sectorsize) {
> if (skipnewfs) {
> fprintf(stderr, "Filesize does not match filesystem sector count\n");
193a196,205
> ftruncate(fd, fssize * sectorsize);
> for(l=0;l< fssize * sectorsize;l += l1) {
> l1 = fssize * sectorsize;
> if (BUFSIZ < l1)
> l1 = BUFSIZ;
> if (l1 != write(fd,buf,l1)) {
> perror(filename);
> exit(12);
> }
> }
218a231,232
> if (skipnewfs == 0) { /* didn't re-indent context so submitted cvs diff would be more readable */
>
701a716,718
>
> } /* endif skipnewfs */
>
Index: newfs.c
===================================================================
RCS file: /src/FreeBSD-CVS/ncvs/src/sbin/newfs/newfs.c,v
retrieving revision 1.18
diff -r1.18 newfs.c
195a196
> int skipnewfs;
237c238
< "NF:T:a:b:c:d:e:f:i:m:o:s:" :
---
> "NF:U:T:a:b:c:d:e:f:i:m:o:s:" :
255a257,259
> case 'U':
> skipnewfs = 1;
> /* fall through */
Index: mfs_vfsops.c
===================================================================
RCS file: /src/FreeBSD-CVS/ncvs/src/sys/ufs/mfs/mfs_vfsops.c,v
retrieving revision 1.41
diff -r1.41 mfs_vfsops.c
48a49,50
> #include <sys/sysproto.h> /* for msync_args */
> #include <sys/mman.h> /* for msync_args */
432a435,441
> /*
> * must mark the calling process as a system process
> * so the pager doesn't try to kill it. Doh! And the
> * pager may because the resident set size may be huge.
> */
> p->p_flag |= P_SYSTEM;
>
471c480,481
< * EINTR/ERESTART.
---
> * EINTR/ERESTART. It will return EWOULDBLOCK if the timer
> * expired.
482,483c492,495
< }
< else if (tsleep((caddr_t)vp, mfs_pri, "mfsidl", 0))
---
> } else {
> int r = tsleep((caddr_t)vp, mfs_pri, "mfsidl", hz * 10);
>
> if (r && r != EWOULDBLOCK)
484a497,522
> }
>
> /*
> * we should call msync on the backing store every 30 seconds,
> * otherwise the pages are not associated with the file and guess
> * what! the syncer never sees them. msync has no effect
> * if the backing store is swap, but a big effect if it's a file
> * (e.g. an NFS mounted file).
> */
> {
> static long lsec;
> int dt = time_second - lsec;
>
> if (dt < -30 || dt > 30) {
> struct msync_args uap;
>
> lsec = time_second;
>
> uap.addr = mfsp->mfs_baseoff;
> uap.len = mfsp->mfs_size;
> uap.flags = MS_ASYNC;
>
> msync(curproc, &uap);
> }
> }
>
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