Author: mckusick
Date: Thu Aug 27 22:14:58 2020
New Revision: 364895
URL: https://svnweb.freebsd.org/changeset/base/364895
Log:
Add a comment to clarify when and why cached names are deleted
during pathname lookup.
Reviewed by: kib
MFC after: 3 days
Sponsored by: Netflix
Modified:
head/sys/kern/vfs_lookup.c
Modified: head/sys/kern/vfs_lookup.c
==============================================================================
--- head/sys/kern/vfs_lookup.c Thu Aug 27 21:47:43 2020 (r364894)
+++ head/sys/kern/vfs_lookup.c Thu Aug 27 22:14:58 2020 (r364895)
@@ -785,6 +785,16 @@ lookup(struct nameidata *ndp)
wantparent = cnp->cn_flags & (LOCKPARENT | WANTPARENT);
KASSERT(cnp->cn_nameiop == LOOKUP || wantparent,
("CREATE, DELETE, RENAME require LOCKPARENT or WANTPARENT."));
+ /*
+ * When set to zero, docache causes the last component of the
+ * pathname to be deleted from the cache and the full lookup
+ * of the name to be done (via VOP_CACHEDLOOKUP()). Often
+ * filesystems need some pre-computed values that are made
+ * during the full lookup, for instance UFS sets dp->i_offset.
+ *
+ * The docache variable is set to zero when requested by the
+ * NOCACHE flag and for all modifying operations except CREATE.
+ */
docache = (cnp->cn_flags & NOCACHE) ^ NOCACHE;
if (cnp->cn_nameiop == DELETE ||
(wantparent && cnp->cn_nameiop != CREATE &&
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