xfs: create a blob array data structure

Create a simple 'blob array' data structure for storage of arbitrarily
sized metadata objects that will be used to reconstruct metadata.  For
the intended usage (temporarily storing extended attribute names and
values) we only have to support storing objects and retrieving them.
Use the xfile abstraction to store the attribute information in memory
that can be swapped out.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

3 files changed, 168 insertions, 0 deletions

diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
index b8d69d206c7a..df35b9286f7a 100644
--- a/fs/xfs/Makefile
+++ b/fs/xfs/Makefile
@@ -175,6 +175,7 @@ xfs-y				+= $(addprefix scrub/, \
 				   agheader_repair.o \
 				   alloc_repair.o \
 				   bitmap.o \
+				   blob.o \
 				   bmap_repair.o \
 				   fscounters_repair.o \
 				   ialloc_repair.o \
diff --git a/fs/xfs/scrub/blob.c b/fs/xfs/scrub/blob.c
new file mode 100644
index 000000000000..3899124b2884
--- /dev/null
+++ b/fs/xfs/scrub/blob.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2021 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_shared.h"
+#include "scrub/array.h"
+#include "scrub/blob.h"
+#include "scrub/xfile.h"
+
+/*
+ * XFS Blob Storage
+ * ================
+ * Stores and retrieves blobs using a memfd object.  Objects are appended to
+ * the file and the offset is returned as a magic cookie for retrieval.
+ */
+
+#define XB_KEY_MAGIC	0xABAADDAD
+struct xb_key {
+	uint32_t		magic;
+	uint32_t		size;
+	loff_t			offset;
+	/* blob comes after here */
+} __packed;
+
+/* Initialize a blob storage object. */
+struct xblob *
+xblob_init(
+	const char	*description)
+{
+	struct xblob	*blob;
+	struct xfile	*xfile;
+	int		error;
+
+	xfile = xfile_create(description, 0);
+	if (IS_ERR(xfile))
+		return ERR_CAST(xfile);
+
+	error = -ENOMEM;
+	blob = kmem_alloc(sizeof(struct xblob), KM_NOFS | KM_MAYFAIL);
+	if (!blob)
+		goto out_xfile;
+
+	blob->xfile = xfile;
+	blob->last_offset = PAGE_SIZE;
+	return blob;
+out_xfile:
+	xfile_destroy(xfile);
+	return ERR_PTR(error);
+}
+
+/* Destroy a blob storage object. */
+void
+xblob_destroy(
+	struct xblob	*blob)
+{
+	xfile_destroy(blob->xfile);
+	kmem_free(blob);
+}
+
+/* Retrieve a blob. */
+int
+xblob_get(
+	struct xblob	*blob,
+	xblob_cookie	cookie,
+	void		*ptr,
+	uint32_t	size)
+{
+	struct xb_key	key;
+	int		error;
+
+	error = xfile_pread(blob->xfile, &key, sizeof(key), cookie);
+	if (error)
+		return error;
+
+	if (key.magic != XB_KEY_MAGIC || key.offset != cookie) {
+		ASSERT(0);
+		return -ENODATA;
+	}
+	if (size < key.size) {
+		ASSERT(0);
+		return -EFBIG;
+	}
+
+	return xfile_pread(blob->xfile, ptr, key.size, cookie + sizeof(key));
+}
+
+/* Store a blob. */
+int
+xblob_put(
+	struct xblob	*blob,
+	xblob_cookie	*cookie,
+	void		*ptr,
+	uint32_t	size)
+{
+	struct xb_key	key = {
+		.offset = blob->last_offset,
+		.magic = XB_KEY_MAGIC,
+		.size = size,
+	};
+	loff_t		pos = blob->last_offset;
+	int		error;
+
+	error = xfile_pwrite(blob->xfile, &key, sizeof(key), pos);
+	if (error)
+		goto out_err;
+
+	pos += sizeof(key);
+	error = xfile_pwrite(blob->xfile, ptr, size, pos);
+	if (error)
+		goto out_err;
+
+	*cookie = blob->last_offset;
+	blob->last_offset += sizeof(key) + size;
+	return 0;
+out_err:
+	xfile_discard(blob->xfile, blob->last_offset, pos - 1);
+	return -ENOMEM;
+}
+
+/* Free a blob. */
+int
+xblob_free(
+	struct xblob	*blob,
+	xblob_cookie	cookie)
+{
+	struct xb_key	key;
+	int		error;
+
+	error = xfile_pread(blob->xfile, &key, sizeof(key), cookie);
+	if (error)
+		return error;
+
+	if (key.magic != XB_KEY_MAGIC || key.offset != cookie) {
+		ASSERT(0);
+		return -ENODATA;
+	}
+
+	xfile_discard(blob->xfile, cookie, cookie + sizeof(key) + key.size - 1);
+	return 0;
+}
diff --git a/fs/xfs/scrub/blob.h b/fs/xfs/scrub/blob.h
new file mode 100644
index 000000000000..106284d7ccf5
--- /dev/null
+++ b/fs/xfs/scrub/blob.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2021 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#ifndef __XFS_SCRUB_BLOB_H__
+#define __XFS_SCRUB_BLOB_H__
+
+struct xblob {
+	struct xfile	*xfile;
+	loff_t		last_offset;
+};
+
+typedef loff_t		xblob_cookie;
+
+struct xblob *xblob_init(const char *descr);
+void xblob_destroy(struct xblob *blob);
+int xblob_get(struct xblob *blob, xblob_cookie cookie, void *ptr,
+		uint32_t size);
+int xblob_put(struct xblob *blob, xblob_cookie *cookie, void *ptr,
+		uint32_t size);
+int xblob_free(struct xblob *blob, xblob_cookie cookie);
+
+#endif /* __XFS_SCRUB_BLOB_H__ */