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@xxxxxxxxxx>
+/*
+ * 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;
+}
--
SUSE Labs, Novell Inc.
-
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
