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-rw-r--r--Documentation/filesystems/vfs.txt90
1 files changed, 68 insertions, 22 deletions
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index ed7e5efc06d8..fbb324e2bd43 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -325,7 +325,8 @@ struct inode_operations {
void * (*follow_link) (struct dentry *, struct nameidata *);
void (*put_link) (struct dentry *, struct nameidata *, void *);
void (*truncate) (struct inode *);
- int (*permission) (struct inode *, int, struct nameidata *);
+ int (*permission) (struct inode *, int, unsigned int);
+ int (*check_acl)(struct inode *, int, unsigned int);
int (*setattr) (struct dentry *, struct iattr *);
int (*getattr) (struct vfsmount *mnt, struct dentry *, struct kstat *);
int (*setxattr) (struct dentry *, const char *,const void *,size_t,int);
@@ -414,6 +415,13 @@ otherwise noted.
permission: called by the VFS to check for access rights on a POSIX-like
filesystem.
+ May be called in rcu-walk mode (flags & IPERM_RCU). If in rcu-walk
+ mode, the filesystem must check the permission without blocking or
+ storing to the inode.
+
+ If a situation is encountered that rcu-walk cannot handle, return
+ -ECHILD and it will be called again in ref-walk mode.
+
setattr: called by the VFS to set attributes for a file. This method
is called by chmod(2) and related system calls.
@@ -534,6 +542,7 @@ struct address_space_operations {
sector_t (*bmap)(struct address_space *, sector_t);
int (*invalidatepage) (struct page *, unsigned long);
int (*releasepage) (struct page *, int);
+ void (*freepage)(struct page *);
ssize_t (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
loff_t offset, unsigned long nr_segs);
struct page* (*get_xip_page)(struct address_space *, sector_t,
@@ -660,11 +669,10 @@ struct address_space_operations {
releasepage: releasepage is called on PagePrivate pages to indicate
that the page should be freed if possible. ->releasepage
should remove any private data from the page and clear the
- PagePrivate flag. It may also remove the page from the
- address_space. If this fails for some reason, it may indicate
- failure with a 0 return value.
- This is used in two distinct though related cases. The first
- is when the VM finds a clean page with no active users and
+ PagePrivate flag. If releasepage() fails for some reason, it must
+ indicate failure with a 0 return value.
+ releasepage() is used in two distinct though related cases. The
+ first is when the VM finds a clean page with no active users and
wants to make it a free page. If ->releasepage succeeds, the
page will be removed from the address_space and become free.
@@ -679,6 +687,12 @@ struct address_space_operations {
need to ensure this. Possibly it can clear the PageUptodate
bit if it cannot free private data yet.
+ freepage: freepage is called once the page is no longer visible in
+ the page cache in order to allow the cleanup of any private
+ data. Since it may be called by the memory reclaimer, it
+ should not assume that the original address_space mapping still
+ exists, and it should not block.
+
direct_IO: called by the generic read/write routines to perform
direct_IO - that is IO requests which bypass the page cache
and transfer data directly between the storage and the
@@ -841,9 +855,12 @@ 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_delete)(struct dentry *);
+ int (*d_hash)(const struct dentry *, const struct inode *,
+ 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 *);
char *(*d_dname)(struct dentry *, char *, int);
@@ -854,13 +871,45 @@ 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_revalidate may be called in rcu-walk mode (nd->flags & LOOKUP_RCU).
+ If in rcu-walk mode, the filesystem must revalidate the dentry without
+ blocking or storing to the dentry, d_parent and d_inode should not be
+ used without care (because they can go NULL), instead nd->inode should
+ be used.
+
+ If a situation is encountered that rcu-walk cannot handle, return
+ -ECHILD and it will be called again in ref-walk mode.
+
+ 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. The inode is the dentry's inode.
+
+ Same locking and synchronisation rules as d_compare regarding
+ what is safe to dereference etc.
+
+ 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.
- d_compare: called when a dentry should be compared with another
+ 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
- deleted. This means no-one is using the dentry, however it is
- still valid and in the dcache
+ 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
+ immediately, or 0 to cache the dentry. Default is NULL which means to
+ always cache a reachable dentry. d_delete must be constant and
+ idempotent.
d_release: called when a dentry is really deallocated
@@ -904,14 +953,11 @@ manipulate dentries:
the usage count)
dput: close a handle for a dentry (decrements the usage count). If
- the usage count drops to 0, the "d_delete" method is called
- and the dentry is placed on the unused list if the dentry is
- still in its parents hash list. Putting the dentry on the
- unused list just means that if the system needs some RAM, it
- goes through the unused list of dentries and deallocates them.
- If the dentry has already been unhashed and the usage count
- drops to 0, in this case the dentry is deallocated after the
- "d_delete" method is called
+ the usage count drops to 0, and the dentry is still in its
+ parent's hash, the "d_delete" method is called to check whether
+ it should be cached. If it should not be cached, or if the dentry
+ is not hashed, it is deleted. Otherwise cached dentries are put
+ into an LRU list to be reclaimed on memory shortage.
d_drop: this unhashes a dentry from its parents hash list. A
subsequent call to dput() will deallocate the dentry if its