On Tue, 2009-03-03 at 22:11 +0900, hooanon05@xxxxxxxxxxx wrote: > Goswin von Brederlow: > > Why? When a page is accessed the filesystem gets a read request and > > reads it either from the RO branch or the delta branch. Why should it > > need to copy up the full file? > > For example, > - you have two mmap for a single file > - the first mapping is done, it may map the file on the lower rdonly > layer > - the other mapping modifies the contents > - can the first mapping see the new content? The lower read-only file would not appear to user-space as the same file at all. It would have its own address space. It clearly would not see the new content. There wouldn't be any problem with reading pages from the lower file for the upper file one at a time as they are faulted. Shaggy -- David Kleikamp IBM Linux Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
