Messages in this thread | | | Date | Thu, 11 Apr 1996 10:49:06 -0500 (CDT) | From | "Christian Holtje <>" <> | Subject | Re: Overmounting a filesystem |
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On Thu, 11 Apr 1996, Graham Mitchell wrote:
> On 10 Apr 96 at 21:43, Christian Holtje docwhat@uiuc wrote: > > <snip> > > > How about this for an off the cuff idea (well...I'm wearing a tee-shirt, > > but still....) > > > > n devices(mountable) /dev/1, /dev/2 ... /dev/n > > mounted on /mnt > > in this order: > > > > mount /dev/1 /mnt > > mount /dev/2 /mnt > > .... > > mount /dev/n /mnt > > > > But you also want to be able to do something like.... > > mount /dev/sr0/<path from root of CD> /usr/src > mount /dev/dha1/<patch from root of HD> /usr/src > > (obviously we'd need to use loopback devices etc for that bits).
Hmmm...in that case, maybe overlay's can be made a special subset of a loopback mount.
> > Flags (sysadmin set): > > > > Reads: > > Getting the directory information in this order: > > Get direntry for this dir (if it exists) for /dev/sr0 > > "" "" for /dev/hda1 > > > Cases to handle: > > If /dev/k has a direntry that matches an > > older direntry(/dev/1.../dev/k-1) then the older one is > > thrown out (therefore inaccessable). > > I'd say the one on the last mounted device should override. > Irrespective of the date. This would allow you to migrate info from > and underlying CDROM up to a hard disk (could be used as a psuedo > archive - all files help on CD, but migrated to faster disk if/when > they're accessed. You'd also need utilities to archive them 'back > down' onto CD).
Whups! That sould read: If /dev/k has a direntry that matches a deventry (starting at /dev/1 to /dev/k-1) then the deventry < k is thrown out, (therefore inaccessable) (i.e. the newer ones take precedence)
> > > > Writes: > > Check if file exists, working /dev/n.../dev/1 Take > > FIRST occurance of a matching dirent. > Again, I'd say that the LAST MOUNTED device should have preference, > then work back onto the previously mounted device if spaec ran out.
Yes....you're write...otherwise the above scheme doesn't make sense... you'd write to a file that gets ignored anyway!
> > > > If file doesn't exist, write to /dev/1 > > > > Cases to handle: > > /dev/k is RO: Try /dev/k+1 till /dev/n then report FS is RO. > > /dev/k doesn't have enought space to write the WHOLE file. > > Write what is possible, continue on /dev/k+1, etc. > > untill you reach the end, then give outofspace error. > > > > When file is closed, move all parts to one /dev/q, > > searching from /dev/1..../dev/n > > > > If not enough space is available, then report an error. > > I dont like the idea of an error being reported long after a file has > possibly been closed my a now dead process.
Yeah...that was my complant too...there must be a way to handle that. Writes should be done differently...have to think about it.
Christian G. Holtje (aka Doctor What)
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