Messages in this thread | | | Date | Sun, 21 Mar 2004 21:11:38 -0800 (PST) | From | Davide Libenzi <> | Subject | Re: [PATCH] cowlinks v2 |
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On 21 Mar 2004, Eric W. Biederman wrote:
> Davide Libenzi <davidel@xmailserver.org> writes: > > > > Actually there is... You don't do the copy until an actual write occurs. > > > Some files are opened read/write when there is simply the chance they might > > > be written to so delaying the copy is generally a win. > > > > What about open+mmap? > > The case is nothing really different from having a hole in your file. > > There are two pieces to implementing this. First you create separate > page cache entries for the cow file and it's original, so the > laziness of mmapped file writes will not bite you.. Second you make > aops -> writepage trigger the actual copy of the file, and have it > return -ENOSPC if you can't do the copy.
There has been a misunderstanding. I thought you were talking about a userspace solution ala fl-cow. Of course if you are inside the kernel you can catch both explicit writes and page syncs.
- Davide
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