Messages in this thread | | | Date | Wed, 16 May 2007 22:07:15 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH] AFS: Implement shared-writable mmap [try #2] |
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David Howells wrote: > Implement shared-writable mmap for AFS. > > The key with which to access the file is obtained from the VMA at the point > where the PTE is made writable by the page_mkwrite() VMA op and cached in the > affected page. > > If there's an outstanding write on the page made with a different key, then > page_mkwrite() will flush it before attaching a record of the new key. > > [try #2] Only flush the page if the page is still part of the mapping (truncate > may have discarded it).
Couple more issues...
> Signed-off-by: David Howells <dhowells@redhat.com>
> +/* > + * notification that a previously read-only page is about to become writable > + * - if it returns an error, the caller will deliver a bus error signal > + * > + * we use this to make a record of the key with which the writeback should be > + * performed and to flush any outstanding writes made with a different key > + * > + * the key to be used is attached to the file pinned by the VMA > + */ > +int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page) > +{ > + struct afs_vnode *vnode = AFS_FS_I(vma->vm_file->f_mapping->host); > + struct key *key = vma->vm_file->private_data; > + int ret; > + > + _enter("{{%x:%u},%x},{%lx}", > + vnode->fid.vid, vnode->fid.vnode, key_serial(key), page->index); > + > + lock_page(page); > + if (page->mapping == vma->vm_file->f_mapping) > + ret = afs_prepare_write(vma->vm_file, page, 0, 0);
I would strongly suggest you used (0, PAGE_CACHE_SIZE) for the range, and have your nopage function DTRT.
Minor issue: you can just check for `if (!page->mapping)` for truncation, which is the usual signal to tell the reader you're checking for truncate. Then you can remove the comment...
> + else > + ret = 0; /* seems truncate interfered - let the caller deal > + * with it (presumably the PTE changed too) */
Rather than add this (not always correct) comment about the VM workings, I'd just add a directive in the page_mkwrite API documentation that the filesystem is to return 0 if the page has been truncated.
> + unlock_page(page); > + > + _leave(" = %d", ret); > + return ret; > +}
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