apfs: begin work on common xfield code

Define apfs_find_xfield() in the new xfield.c file; use it to replace
the ad hoc code that finds extended fields in inodes and dentries.
Creation of xfields will soon be moved to common code as well.

Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>

fs/apfs/Makefile

@@ -7,4 +7,4 @@ obj-$(CONFIG_APFS_FS) += apfs.o
 
 apfs-y := btree.o dir.o extents.o file.o inode.o key.o message.o namei.o \
 	  node.o object.o spaceman.o super.o symlink.o transaction.o \
-	  unicode.o xattr.o
+	  unicode.o xattr.o xfield.o

fs/apfs/dir.c

@@ -16,6 +16,7 @@
 #include "node.h"
 #include "super.h"
 #include "transaction.h"
+#include "xfield.h"
 
 /**
  * apfs_drec_from_query - Read the directory record found by a successful query
@@ -36,6 +37,8 @@ static int apfs_drec_from_query(struct apfs_query *query,
 	struct apfs_drec_hashed_key *de_key;
 	struct apfs_drec_val *de;
 	int namelen = query->key_len - sizeof(*de_key);
+	char *xval = NULL;
+	int xlen;
 
 	if (namelen < 1)
 		return -EFSCORRUPTED;
@@ -54,18 +57,12 @@ static int apfs_drec_from_query(struct apfs_query *query,
 		return -EFSCORRUPTED;
 
 	/* The dentry may have at most one xfield: the sibling id */
-	if (query->len == sizeof(*de)) {
-		drec->sibling_id = 0;
-	} else {
-		int x_meta_len;
-		__le64 *sib_id;
+	drec->sibling_id = 0;
+	xlen = apfs_find_xfield(de->xfields, query->len - sizeof(*de),
+				APFS_DREC_EXT_TYPE_SIBLING_ID, &xval);
+	if (xlen >= sizeof(__le64)) {
+		__le64 *sib_id = (__le64 *)xval;
 
-		x_meta_len = sizeof(struct apfs_xf_blob) +
-			     sizeof(struct apfs_x_field);
-		if (query->len != sizeof(*de) + x_meta_len + sizeof(*sib_id))
-			return -EFSCORRUPTED;
-
-		sib_id = (void *)de->xfields + x_meta_len;
 		drec->sibling_id = le64_to_cpup(sib_id);
 	}
 

fs/apfs/inode.c

@@ -18,6 +18,7 @@
 #include "node.h"
 #include "super.h"
 #include "xattr.h"
+#include "xfield.h"
 
 static int apfs_readpage(struct file *file, struct page *page)
 {
@@ -84,11 +85,9 @@ static int apfs_inode_from_query(struct apfs_query *query, struct inode *inode)
 {
 	struct apfs_inode_info *ai = APFS_I(inode);
 	struct apfs_inode_val *inode_val;
-	struct apfs_dstream *dstream = NULL;
-	struct apfs_xf_blob *xblob;
-	struct apfs_x_field *xfield;
 	char *raw = query->node->object.bh->b_data;
-	int rest, i;
+	char *xval = NULL;
+	int xlen;
 	u32 rdev = 0;
 
 	if (query->len < sizeof(*inode_val))
@@ -121,45 +120,26 @@ static int apfs_inode_from_query(struct apfs_query *query, struct inode *inode)
 	inode->i_mtime = apfs_timespec(inode_val->mod_time);
 	ai->i_crtime = apfs_timespec(inode_val->create_time);
 
-	xblob = (struct apfs_xf_blob *) inode_val->xfields;
-	xfield = (struct apfs_x_field *) xblob->xf_data;
-	rest = query->len - (sizeof(*inode_val) + sizeof(*xblob));
-	rest -= le16_to_cpu(xblob->xf_num_exts) * sizeof(xfield[0]);
-	if (rest < 0)
-		goto corrupted;
-	for (i = 0; i < le16_to_cpu(xblob->xf_num_exts); ++i) {
-		int attrlen;
+	inode->i_size = inode->i_blocks = 0; /* TODO: compressed inodes */
+	xlen = apfs_find_xfield(inode_val->xfields,
+				query->len - sizeof(*inode_val),
+				APFS_INO_EXT_TYPE_DSTREAM, &xval);
+	if (xlen >= sizeof(struct apfs_dstream)) {
+		struct apfs_dstream *dstream = (struct apfs_dstream *)xval;
 
-		/* Attribute length is padded to a multiple of 8 */
-		attrlen = round_up(le16_to_cpu(xfield[i].x_size), 8);
-		if (attrlen > rest)
-			break;
-
-		/* These are the only xfields we care about, for now */
-		if (xfield[i].x_type == APFS_INO_EXT_TYPE_DSTREAM) {
-			dstream = (struct apfs_dstream *)
-					((char *)inode_val + query->len - rest);
-			break;
-		}
-		if (xfield[i].x_type == APFS_INO_EXT_TYPE_RDEV) {
-			__le32 *rdev_p = (void *)inode_val + query->len - rest;
-
-			rdev = le32_to_cpu(*rdev_p);
-		}
-
-		rest -= attrlen;
-	}
-
-	if (dstream) {
 		inode->i_size = le64_to_cpu(dstream->size);
 		inode->i_blocks = le64_to_cpu(dstream->alloced_size) >> 9;
-	} else {
-		/*
-		 * This inode is "empty", but it may actually hold compressed
-		 * data in the named attribute com.apple.decmpfs, and sometimes
-		 * in com.apple.ResourceFork
-		 */
-		inode->i_size = inode->i_blocks = 0;
+	}
+	xval = NULL;
+
+	rdev = 0;
+	xlen = apfs_find_xfield(inode_val->xfields,
+				query->len - sizeof(*inode_val),
+				APFS_INO_EXT_TYPE_RDEV, &xval);
+	if (xlen >= sizeof(__le32)) {
+		__le32 *rdev_p = (__le32 *)xval;
+
+		rdev = le32_to_cpup(rdev_p);
 	}
 
 	apfs_inode_set_ops(inode, rdev);

fs/apfs/inode.h

@@ -49,52 +49,6 @@ struct apfs_inode_val {
 /*5C*/	u8 xfields[];
 } __packed;
 
-/* Extended field types */
-#define APFS_DREC_EXT_TYPE_SIBLING_ID 1
-
-#define APFS_INO_EXT_TYPE_SNAP_XID 1
-#define APFS_INO_EXT_TYPE_DELTA_TREE_OID 2
-#define APFS_INO_EXT_TYPE_DOCUMENT_ID 3
-#define APFS_INO_EXT_TYPE_NAME 4
-#define APFS_INO_EXT_TYPE_PREV_FSIZE 5
-#define APFS_INO_EXT_TYPE_RESERVED_6 6
-#define APFS_INO_EXT_TYPE_FINDER_INFO 7
-#define APFS_INO_EXT_TYPE_DSTREAM 8
-#define APFS_INO_EXT_TYPE_RESERVED_9 9
-#define APFS_INO_EXT_TYPE_DIR_STATS_KEY 10
-#define APFS_INO_EXT_TYPE_FS_UUID 11
-#define APFS_INO_EXT_TYPE_RESERVED_12 12
-#define APFS_INO_EXT_TYPE_SPARSE_BYTES 13
-#define APFS_INO_EXT_TYPE_RDEV 14
-
-/* Extended field flags */
-#define APFS_XF_DATA_DEPENDENT		0x01
-#define APFS_XF_DO_NOT_COPY		0x02
-#define APFS_XF_RESERVED_4		0x04
-#define APFS_XF_CHILDREN_INHERIT	0x08
-#define APFS_XF_USER_FIELD		0x10
-#define APFS_XF_SYSTEM_FIELD		0x20
-#define APFS_XF_RESERVED_40		0x40
-#define APFS_XF_RESERVED_80		0x80
-
-/*
- * Structure used to store the number and size of extended fields of an inode
- */
-struct apfs_xf_blob {
-	__le16 xf_num_exts;
-	__le16 xf_used_data;
-	u8 xf_data[];
-} __packed;
-
-/*
- * Structure used to store an inode's extended field
- */
-struct apfs_x_field {
-	u8 x_type;
-	u8 x_flags;
-	__le16 x_size;
-} __packed;
-
 /*
  * Structure of a data stream record
  */

fs/apfs/xfield.c

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/apfs/xfield.c
+ *
+ * Copyright (C) 2019 Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
+ */
+
+#include <linux/kernel.h>
+#include "xfield.h"
+
+/**
+ * apfs_find_xfield - Find an extended field value in an inode or dentry record
+ * @xfields:	pointer to the on-disk xfield collection for the record
+ * @len:	length of the collection
+ * @xtype:	type of the xfield to retrieve
+ * @xval:	on return, a pointer to the wanted on-disk xfield value
+ *
+ * Returns the length of @xval on success, or 0 if no matching xfield was found;
+ * the caller must check that the expected structures fit before casting @xval.
+ */
+int apfs_find_xfield(u8 *xfields, int len, u8 xtype, char **xval)
+{
+	struct apfs_xf_blob *blob;
+	struct apfs_x_field *xfield;
+	int count;
+	int rest = len;
+	int i;
+
+	if (!len)
+		return 0; /* No xfield data */
+
+	rest -= sizeof(*blob);
+	if (rest < 0)
+		return 0; /* Corruption */
+	blob = (struct apfs_xf_blob *)xfields;
+
+	count = le16_to_cpu(blob->xf_num_exts);
+	rest -= count * sizeof(*xfield);
+	if (rest < 0)
+		return 0; /* Corruption */
+	xfield = (struct apfs_x_field *)blob->xf_data;
+
+	for (i = 0; i < count; ++i) {
+		int xlen;
+
+		/* Attribute length is padded to a multiple of 8 */
+		xlen = round_up(le16_to_cpu(xfield[i].x_size), 8);
+		if (xlen > rest)
+			return 0; /* Corruption */
+
+		if (xfield[i].x_type == xtype) {
+			*xval = (char *)xfields + len - rest;
+			return xlen;
+		}
+		rest -= xlen;
+	}
+	return 0;
+}

fs/apfs/xfield.h

@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *  linux/fs/apfs/xfield.h
+ *
+ * Copyright (C) 2019 Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
+ */
+
+#ifndef _APFS_XFIELD_H
+#define _APFS_XFIELD_H
+
+#include <linux/types.h>
+
+/* Extended field types for dentries */
+#define APFS_DREC_EXT_TYPE_SIBLING_ID 1
+
+/* Extended field types for inodes */
+#define APFS_INO_EXT_TYPE_SNAP_XID 1
+#define APFS_INO_EXT_TYPE_DELTA_TREE_OID 2
+#define APFS_INO_EXT_TYPE_DOCUMENT_ID 3
+#define APFS_INO_EXT_TYPE_NAME 4
+#define APFS_INO_EXT_TYPE_PREV_FSIZE 5
+#define APFS_INO_EXT_TYPE_RESERVED_6 6
+#define APFS_INO_EXT_TYPE_FINDER_INFO 7
+#define APFS_INO_EXT_TYPE_DSTREAM 8
+#define APFS_INO_EXT_TYPE_RESERVED_9 9
+#define APFS_INO_EXT_TYPE_DIR_STATS_KEY 10
+#define APFS_INO_EXT_TYPE_FS_UUID 11
+#define APFS_INO_EXT_TYPE_RESERVED_12 12
+#define APFS_INO_EXT_TYPE_SPARSE_BYTES 13
+#define APFS_INO_EXT_TYPE_RDEV 14
+
+/* Extended field flags */
+#define APFS_XF_DATA_DEPENDENT		0x01
+#define APFS_XF_DO_NOT_COPY		0x02
+#define APFS_XF_RESERVED_4		0x04
+#define APFS_XF_CHILDREN_INHERIT	0x08
+#define APFS_XF_USER_FIELD		0x10
+#define APFS_XF_SYSTEM_FIELD		0x20
+#define APFS_XF_RESERVED_40		0x40
+#define APFS_XF_RESERVED_80		0x80
+
+/*
+ * Structure used to store the number and size of an xfield collection
+ */
+struct apfs_xf_blob {
+	__le16 xf_num_exts;
+	__le16 xf_used_data;
+	u8 xf_data[];
+} __packed;
+
+/*
+ * Structure used to describe an extended field
+ */
+struct apfs_x_field {
+	u8 x_type;
+	u8 x_flags;
+	__le16 x_size;
+} __packed;
+
+extern int apfs_find_xfield(u8 *xfields, int len, u8 xtype, char **xval);
+
+#endif	/* _APFS_XFIELD_H */