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fs: change d_compare for rcu-walk

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Change d_compare so it may be called from lock-free RCU lookups. This
does put significant restrictions on what may be done from the callback,
however there don't seem to have been any problems with in-tree fses.
If some strange use case pops up that _really_ cannot cope with the
rcu-walk rules, we can just add new rcu-unaware callbacks, which would
cause name lookup to drop out of rcu-walk mode.

For in-tree filesystems, this is just a mechanical change.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>
This commit is contained in:
Nick Piggin
2011-01-07 17:49:27 +11:00
parent fb2d5b86af
commit 621e155a35
23 changed files with 242 additions and 157 deletions
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4
Documentation/filesystems/Locking
View File

@@ -11,7 +11,9 @@ be able to use diff(1).
prototypes:
int (*d_revalidate)(struct dentry *, int);
int (*d_hash) (struct dentry *, struct qstr *);
int (*d_compare) (struct dentry *, struct qstr *, struct qstr *);
int (*d_compare)(const struct dentry *, const struct inode *,
const struct dentry *, const struct inode *,
unsigned int, const char *, const struct qstr *);
int (*d_delete)(struct dentry *);
void (*d_release)(struct dentry *);
void (*d_iput)(struct dentry *, struct inode *);

7
Documentation/filesystems/porting
View File

@@ -326,3 +326,10 @@ to it.
unreferenced dentries, and is now only called when the dentry refcount goes to
0. Even on 0 refcount transition, it must be able to tolerate being called 0,
1, or more times (eg. constant, idempotent).
---
[mandatory]
.d_compare() calling convention and locking rules are significantly
changed. Read updated documentation in Documentation/filesystems/vfs.txt (and
look at examples of other filesystems) for guidance.

26
Documentation/filesystems/vfs.txt
View File

@@ -848,7 +848,9 @@ defined:
struct dentry_operations {
int (*d_revalidate)(struct dentry *, struct nameidata *);
int (*d_hash)(struct dentry *, struct qstr *);
int (*d_compare)(struct dentry *, struct qstr *, struct qstr *);
int (*d_compare)(const struct dentry *, const struct inode *,
const struct dentry *, const struct inode *,
unsigned int, const char *, const struct qstr *);
int (*d_delete)(const struct dentry *);
void (*d_release)(struct dentry *);
void (*d_iput)(struct dentry *, struct inode *);
@@ -860,9 +862,27 @@ struct dentry_operations {
dcache. Most filesystems leave this as NULL, because all their
dentries in the dcache are valid
d_hash: called when the VFS adds a dentry to the hash table
d_hash: called when the VFS adds a dentry to the hash table. The first
dentry passed to d_hash is the parent directory that the name is
to be hashed into.
d_compare: called when a dentry should be compared with another
d_compare: called to compare a dentry name with a given name. The first
dentry is the parent of the dentry to be compared, the second is
the parent's inode, then the dentry and inode (may be NULL) of the
child dentry. len and name string are properties of the dentry to be
compared. qstr is the name to compare it with.
Must be constant and idempotent, and should not take locks if
possible, and should not or store into the dentry or inodes.
Should not dereference pointers outside the dentry or inodes without
lots of care (eg. d_parent, d_inode, d_name should not be used).
However, our vfsmount is pinned, and RCU held, so the dentries and
inodes won't disappear, neither will our sb or filesystem module.
->i_sb and ->d_sb may be used.
It is a tricky calling convention because it needs to be called under
"rcu-walk", ie. without any locks or references on things.
d_delete: called when the last reference to a dentry is dropped and the
dcache is deciding whether or not to cache it. Return 1 to delete