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gentoo_bender
n00b
Joined: 19 May 2005
Posts: 1
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 Posted: Thu May 19, 2005 2:10 pm Post subject: unionfs problems - why does union become read-only? |
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Hello,
I am currently trying to transparently mount a part of my filesystem in memory and use unionfs to merge it with the hdd filesystem.
The problem I'm facing is the following: I want the ram part of the filesystem to be read-only and the hdd part to be read-write - where files present in ram should overlap files on hdd. The union should be read-write, i.e. changes to files should be written directly to disk, not to ram.
So, for example if /hd is the part on disk and /ram is the ram-part, and I store the union in /union, I would use:
| Code: | | # mount -t unionfs -o dirs="/ram=ro:/hd" none /union |
This does work (ram files overlap disc files), but /union is read-only this way.. (although mount says it"s rw) 
If I do it the other way round:
| Code: | | # mount -t unionfs -o dirs="/hd:/ram=ro" none /union |
then /union is read-write, but files in /ram do not overlap files in /hd (actually it's the other way round..)
So somehow the rw-setting of the first directory determines the rw-setting of the union in this case. I couldn't find any info in the manpages about this. Can this behaviour be changed?
What I mean with overlap: if there is a file /hd/afile and a file /ram/afile then /union/afile preferrably accesses /ram/afile (for read-access) and /hd/afile only for write-access. |
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TrueDFX
Retired Dev
Joined: 02 Jun 2004
Posts: 1348
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| Posted: Thu May 19, 2005 3:20 pm Post subject: Re: unionfs problems - why does union become read-only? |
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Hi, | gentoo_bender wrote: | | What I mean with overlap: if there is a file /hd/afile and a file /ram/afile then /union/afile preferrably accesses /ram/afile (for read-access) and /hd/afile only for write-access. |
This would mean that if a file is read when opened for both reading and writing at once, you will see different results from when it is read when opened only for reading. Have you thought about the problems this may cause carefully? |
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