afs: Get an AFS3 ACL as an xattr

Implement an xattr on AFS files called "afs.acl" that retrieves a file's
ACL.  It returns the raw AFS3 ACL from the result of calling FS.FetchACL,
leaving any interpretation to userspace.

Note that whilst YFS servers will respond to FS.FetchACL, this will render
a more-advanced YFS ACL down.  Use "afs.yfs.acl" instead for that.
Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/afs_fs.h

@@ -17,6 +17,7 @@
 
 enum AFS_FS_Operations {
 	FSFETCHDATA		= 130,	/* AFS Fetch file data */
+	FSFETCHACL		= 131,	/* AFS Fetch file ACL */
 	FSFETCHSTATUS		= 132,	/* AFS Fetch file status */
 	FSSTOREDATA		= 133,	/* AFS Store file data */
 	FSSTORESTATUS		= 135,	/* AFS Store file status */

fs/afs/fsclient.c

@@ -2391,3 +2391,125 @@ int afs_fs_inline_bulk_status(struct afs_fs_cursor *fc,
 	afs_make_call(&fc->ac, call, GFP_NOFS);
 	return afs_wait_for_call_to_complete(call, &fc->ac);
 }
+
+/*
+ * deliver reply data to an FS.FetchACL
+ */
+static int afs_deliver_fs_fetch_acl(struct afs_call *call)
+{
+	struct afs_vnode *vnode = call->reply[1];
+	struct afs_acl *acl;
+	const __be32 *bp;
+	unsigned int size;
+	int ret;
+
+	_enter("{%u}", call->unmarshall);
+
+	switch (call->unmarshall) {
+	case 0:
+		afs_extract_to_tmp(call);
+		call->unmarshall++;
+
+		/* extract the returned data length */
+	case 1:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		size = call->count2 = ntohl(call->tmp);
+		size = round_up(size, 4);
+
+		acl = kmalloc(struct_size(acl, data, size), GFP_KERNEL);
+		if (!acl)
+			return -ENOMEM;
+		call->reply[0] = acl;
+		acl->size = call->count2;
+		afs_extract_begin(call, acl->data, size);
+		call->unmarshall++;
+
+		/* extract the returned data */
+	case 2:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		afs_extract_to_buf(call, (21 + 6) * 4);
+		call->unmarshall++;
+
+		/* extract the metadata */
+	case 3:
+		ret = afs_extract_data(call, false);
+		if (ret < 0)
+			return ret;
+
+		bp = call->buffer;
+		ret = afs_decode_status(call, &bp, &vnode->status, vnode,
+					&vnode->status.data_version, NULL);
+		if (ret < 0)
+			return ret;
+		xdr_decode_AFSVolSync(&bp, call->reply[2]);
+
+		call->unmarshall++;
+
+	case 4:
+		break;
+	}
+
+	_leave(" = 0 [done]");
+	return 0;
+}
+
+static void afs_destroy_fs_fetch_acl(struct afs_call *call)
+{
+	kfree(call->reply[0]);
+	afs_flat_call_destructor(call);
+}
+
+/*
+ * FS.FetchACL operation type
+ */
+static const struct afs_call_type afs_RXFSFetchACL = {
+	.name		= "FS.FetchACL",
+	.op		= afs_FS_FetchACL,
+	.deliver	= afs_deliver_fs_fetch_acl,
+	.destructor	= afs_destroy_fs_fetch_acl,
+};
+
+/*
+ * Fetch the ACL for a file.
+ */
+struct afs_acl *afs_fs_fetch_acl(struct afs_fs_cursor *fc)
+{
+	struct afs_vnode *vnode = fc->vnode;
+	struct afs_call *call;
+	struct afs_net *net = afs_v2net(vnode);
+	__be32 *bp;
+
+	_enter(",%x,{%llx:%llu},,",
+	       key_serial(fc->key), vnode->fid.vid, vnode->fid.vnode);
+
+	call = afs_alloc_flat_call(net, &afs_RXFSFetchACL, 16, (21 + 6) * 4);
+	if (!call) {
+		fc->ac.error = -ENOMEM;
+		return ERR_PTR(-ENOMEM);
+	}
+
+	call->key = fc->key;
+	call->reply[0] = NULL;
+	call->reply[1] = vnode;
+	call->reply[2] = NULL; /* volsync */
+	call->ret_reply0 = true;
+
+	/* marshall the parameters */
+	bp = call->request;
+	bp[0] = htonl(FSFETCHACL);
+	bp[1] = htonl(vnode->fid.vid);
+	bp[2] = htonl(vnode->fid.vnode);
+	bp[3] = htonl(vnode->fid.unique);
+
+	call->cb_break = fc->cb_break;
+	afs_use_fs_server(call, fc->cbi);
+	trace_afs_make_fs_call(call, &vnode->fid);
+	afs_make_call(&fc->ac, call, GFP_KERNEL);
+	return (struct afs_acl *)afs_wait_for_call_to_complete(call, &fc->ac);
+}

fs/afs/internal.h

@@ -977,6 +977,13 @@ extern int afs_fs_fetch_status(struct afs_fs_cursor *, struct afs_net *,
 			       struct afs_fid *, struct afs_file_status *,
 			       struct afs_callback *, struct afs_volsync *);
 
+struct afs_acl {
+	u32	size;
+	u8	data[];
+};
+
+extern struct afs_acl *afs_fs_fetch_acl(struct afs_fs_cursor *);
+
 /*
  * fs_probe.c
  */

fs/afs/xattr.c

@@ -16,6 +16,7 @@
 #include "internal.h"
 
 static const char afs_xattr_list[] =
+	"afs.acl\0"
 	"afs.cell\0"
 	"afs.fid\0"
 	"afs.volume";
@@ -33,6 +34,57 @@ ssize_t afs_listxattr(struct dentry *dentry, char *buffer, size_t size)
 	return sizeof(afs_xattr_list);
 }
 
+/*
+ * Get a file's ACL.
+ */
+static int afs_xattr_get_acl(const struct xattr_handler *handler,
+			     struct dentry *dentry,
+			     struct inode *inode, const char *name,
+			     void *buffer, size_t size)
+{
+	struct afs_fs_cursor fc;
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	struct afs_acl *acl = NULL;
+	struct key *key;
+	int ret;
+
+	key = afs_request_key(vnode->volume->cell);
+	if (IS_ERR(key))
+		return PTR_ERR(key);
+
+	ret = -ERESTARTSYS;
+	if (afs_begin_vnode_operation(&fc, vnode, key)) {
+		while (afs_select_fileserver(&fc)) {
+			fc.cb_break = afs_calc_vnode_cb_break(vnode);
+			acl = afs_fs_fetch_acl(&fc);
+		}
+
+		afs_check_for_remote_deletion(&fc, fc.vnode);
+		afs_vnode_commit_status(&fc, vnode, fc.cb_break);
+		ret = afs_end_vnode_operation(&fc);
+	}
+
+	if (ret == 0) {
+		ret = acl->size;
+		if (size > 0) {
+			ret = -ERANGE;
+			if (acl->size > size)
+				return -ERANGE;
+			memcpy(buffer, acl->data, acl->size);
+			ret = acl->size;
+		}
+		kfree(acl);
+	}
+
+	key_put(key);
+	return ret;
+}
+
+static const struct xattr_handler afs_xattr_afs_acl_handler = {
+	.name	= "afs.acl",
+	.get	= afs_xattr_get_acl,
+};
+
 /*
  * Get the name of the cell on which a file resides.
  */
@@ -123,6 +175,7 @@ static const struct xattr_handler afs_xattr_afs_volume_handler = {
 };
 
 const struct xattr_handler *afs_xattr_handlers[] = {
+	&afs_xattr_afs_acl_handler,
 	&afs_xattr_afs_cell_handler,
 	&afs_xattr_afs_fid_handler,
 	&afs_xattr_afs_volume_handler,

include/trace/events/afs.h

@@ -33,6 +33,7 @@ enum afs_call_trace {
 
 enum afs_fs_operation {
 	afs_FS_FetchData		= 130,	/* AFS Fetch file data */
+	afs_FS_FetchACL			= 131,	/* AFS Fetch file ACL */
 	afs_FS_FetchStatus		= 132,	/* AFS Fetch file status */
 	afs_FS_StoreData		= 133,	/* AFS Store file data */
 	afs_FS_StoreStatus		= 135,	/* AFS Store file status */