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-rw-r--r--fs/bcachefs/dirent_format.h42
1 files changed, 42 insertions, 0 deletions
diff --git a/fs/bcachefs/dirent_format.h b/fs/bcachefs/dirent_format.h
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+++ b/fs/bcachefs/dirent_format.h
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+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_DIRENT_FORMAT_H
+#define _BCACHEFS_DIRENT_FORMAT_H
+
+/*
+ * Dirents (and xattrs) have to implement string lookups; since our b-tree
+ * doesn't support arbitrary length strings for the key, we instead index by a
+ * 64 bit hash (currently truncated sha1) of the string, stored in the offset
+ * field of the key - using linear probing to resolve hash collisions. This also
+ * provides us with the readdir cookie posix requires.
+ *
+ * Linear probing requires us to use whiteouts for deletions, in the event of a
+ * collision:
+ */
+
+struct bch_dirent {
+ struct bch_val v;
+
+ /* Target inode number: */
+ union {
+ __le64 d_inum;
+ struct { /* DT_SUBVOL */
+ __le32 d_child_subvol;
+ __le32 d_parent_subvol;
+ };
+ };
+
+ /*
+ * Copy of mode bits 12-15 from the target inode - so userspace can get
+ * the filetype without having to do a stat()
+ */
+ __u8 d_type;
+
+ __u8 d_name[];
+} __packed __aligned(8);
+
+#define DT_SUBVOL 16
+#define BCH_DT_MAX 17
+
+#define BCH_NAME_MAX 512
+
+#endif /* _BCACHEFS_DIRENT_FORMAT_H */