afs: Maintain netfs_i_context::remote_i_size

Make afs use netfslib's tracking for the server's idea of what the current
inode size is independently of inode->i_size.  We really want to use this
value when calculating the new vnode size when initiating a StoreData RPC
op rather than the size stat() presents to the user (ie. inode->i_size) as
the latter is affected by as-yet uncommitted writes.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-afs@lists.infradead.org

Link: https://lore.kernel.org/r/164623014626.3564931.8375344024648265358.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/164678220204.1200972.17408022517463940584.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/164692923592.2099075.5466132542956550401.stgit@warthog.procyon.org.uk/ # v3

Author: dhowells

fs/afs/inode.c

@@ -246,6 +246,7 @@ static void afs_apply_status(struct afs_operation *op,
 		 * idea of what the size should be that's not the same as
 		 * what's on the server.
 		 */
+		vnode->netfs_ctx.remote_i_size = status->size;
 		if (change_size) {
 			afs_set_i_size(vnode, status->size);
 			inode->i_ctime = t;

fs/afs/write.c

@@ -353,9 +353,10 @@ static const struct afs_operation_ops afs_store_data_operation = {
 static int afs_store_data(struct afs_vnode *vnode, struct iov_iter *iter, loff_t pos,
 			  bool laundering)
 {
+	struct netfs_i_context *ictx = &vnode->netfs_ctx;
 	struct afs_operation *op;
 	struct afs_wb_key *wbk = NULL;
-	loff_t size = iov_iter_count(iter), i_size;
+	loff_t size = iov_iter_count(iter);
 	int ret = -ENOKEY;
 
 	_enter("%s{%llx:%llu.%u},%llx,%llx",
@@ -377,15 +378,13 @@ static int afs_store_data(struct afs_vnode *vnode, struct iov_iter *iter, loff_t
 		return -ENOMEM;
 	}
 
-	i_size = i_size_read(&vnode->vfs_inode);
-
 	afs_op_set_vnode(op, 0, vnode);
 	op->file[0].dv_delta = 1;
 	op->file[0].modification = true;
 	op->store.write_iter = iter;
 	op->store.pos = pos;
 	op->store.size = size;
-	op->store.i_size = max(pos + size, i_size);
+	op->store.i_size = max(pos + size, ictx->remote_i_size);
 	op->store.laundering = laundering;
 	op->mtime = vnode->vfs_inode.i_mtime;
 	op->flags |= AFS_OPERATION_UNINTR;