Dentry

Directory entry. More...

Collaboration diagram for Dentry:

Detailed Description

Directory entry.

A dentry represents the actual name in the filesystem hierarchy. It can be either positive, meaning it has an associated inode, or negative, meaning it does not have an associated inode.

Mountpoints and Root Dentries

The difference between a mountpoint dentry and a root dentry can be a bit confusing, so here is a quick explanation. When a filesystem is mounted the dentry that it gets mounted to becomes a mountpoint, any data that was there before becomes hidden and when we traverse to that dentry we "jump" to the root dentry of the mounted filesystem. The root dentry of the mounted filesystem is simply the root directory of that filesystem.

This means that the mountpoint does not "become" the root of the mounted filesystem, it simply points to it.

Finally, note that just becouse a dentry is a mountpoint does not mean that it can be traversed by the current process, a process can only traverse a mountpoint if it is visible in its namespace, if its not visible the dentry acts exactly like a normal dentry.

Data Structures
struct	dentry_ops_t
	Dentry operations structure. More...
struct	dentry_t
	Directory entry structure. More...

Macros
#define	DENTRY_IS_ROOT(dentry)   ((dentry)->parent == (dentry))
	Macro to check if a dentry is the root entry in its filesystem.

Typedefs
typedef uint64_t	dentry_id_t
	Dentry ID type.

Enumerations
enum	dentry_flags_t { DENTRY_NEGATIVE = 1 << 0 }
	Dentry flags. More...

Functions
dentry_t *	dentry_new (superblock_t *superblock, dentry_t *parent, const char *name)
	Create a new dentry.
dentry_t *	dentry_get (const dentry_t *parent, const char *name)
	Get a dentry for the given name. Will NOT traverse mountpoints.
dentry_t *	dentry_lookup (const path_t *parent, const char *name)
	Lookup a dentry for the given name. Will NOT traverse mountpoints.
void	dentry_make_positive (dentry_t *dentry, inode_t *inode)
	Make a dentry positive by associating it with an inode.
bool	dentry_is_positive (dentry_t *dentry)
	Check if a dentry is positive.
bool	dentry_is_file (dentry_t *dentry)
	Check if the inode associated with a dentry is a file.
bool	dentry_is_dir (dentry_t *dentry)
	Check if the inode associated with a dentry is a directory.
uint64_t	dentry_generic_getdents (dentry_t *dentry, dirent_t *buffer, uint64_t count, uint64_t *offset, mode_t mode)
	Helper function for a basic getdents.

Macro Definition Documentation

DENTRY_IS_ROOT

#define DENTRY_IS_ROOT

(

dentry

)

((dentry)->parent == (dentry))

Macro to check if a dentry is the root entry in its filesystem.

A dentry is considered the root if its parent is itself.

Parameters

dentry

The dentry to check.

Returns

true if the dentry is the root, false otherwise.

Definition at line 65 of file dentry.h.

Typedef Documentation

dentry_id_t

typedef uint64_t dentry_id_t

Dentry ID type.

Definition at line 55 of file dentry.h.

Enumeration Type Documentation

dentry_flags_t

enum dentry_flags_t

Dentry flags.

Enumerator
DENTRY_NEGATIVE	Dentry is negative (no associated inode).

Definition at line 47 of file dentry.h.

Function Documentation

dentry_new()

dentry_t * dentry_new	(	superblock_t *	superblock,
		dentry_t *	parent,
		const char *	name
	)

Create a new dentry.

Will not add the dentry to its parent's list of children but it will appear in the dentry cache as a negative dentry until dentry_make_positive() is called making it positive. This is needed to solve some race conditions when creating new files. While the dentry is negative it is not possible to create another dentry of the same name in the same parent, and any lookup to the dentry will fail until it is made positive.

There is no dentry_free() instead use UNREF().

Parameters

superblock	The superblock the dentry belongs to.
parent	The parent dentry, can be NULL if this is a root dentry.
name	The name of the dentry.

Returns

On success, the new dentry. On failure, returns NULL and errno is set.

Definition at line 114 of file dentry.c.

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dentry_get()

dentry_t * dentry_get	(	const dentry_t *	parent,
		const char *	name
	)

Get a dentry for the given name. Will NOT traverse mountpoints.

Will only check the dentry cache and return a dentry if it exists there, will not call the filesystem's lookup function.

Parameters

parent	The parent path.
name	The name of the dentry.

Returns

On success, the dentry, might be negative. On failure, returns NULL and errno is set.

Definition at line 164 of file dentry.c.

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dentry_lookup()

dentry_t * dentry_lookup	(	const path_t *	parent,
		const char *	name
	)

Lookup a dentry for the given name. Will NOT traverse mountpoints.

If the dentry is not found in the dentry cache, the filesystem's lookup function will be called to try to find it.

Parameters

parent	The parent path.
name	The name of the dentry.

Returns

On success, the dentry, might be negative. On failure, returns NULL and errno is set.

Definition at line 176 of file dentry.c.

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dentry_make_positive()

void dentry_make_positive	(	dentry_t *	dentry,
		inode_t *	inode
	)

Make a dentry positive by associating it with an inode.

This function is expected to be protected by the parent inode's mutex.

Parameters

dentry	The dentry to make positive, or NULL for no-op.
inode	The inode to associate with the dentry, or NULL for no-op.

Definition at line 226 of file dentry.c.

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dentry_is_positive()

bool dentry_is_positive

(

dentry_t *

dentry

)

Check if a dentry is positive.

Parameters

dentry

The dentry to check.

Returns

true if the dentry is positive, false if it is negative.

Definition at line 243 of file dentry.c.

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dentry_is_file()

bool dentry_is_file

(

dentry_t *

dentry

)

Check if the inode associated with a dentry is a file.

Parameters

dentry

The dentry to check.

Returns

true if the dentry is a file, false otherwise or if the dentry is negative.

Definition at line 253 of file dentry.c.

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dentry_is_dir()

bool dentry_is_dir

(

dentry_t *

dentry

)

Check if the inode associated with a dentry is a directory.

Parameters

dentry

The dentry to check.

Returns

true if the dentry is a directory, false otherwise or if the dentry is negative.

Definition at line 268 of file dentry.c.

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dentry_generic_getdents()

uint64_t dentry_generic_getdents	(	dentry_t *	dentry,
		dirent_t *	buffer,
		uint64_t	count,
		uint64_t *	offset,
		mode_t	mode
	)

Helper function for a basic getdents.

This function can be used by filesystems that do not have any special requirements for getdents.

In practice this is only useful for in-memory filesystems.

Used by setting the dentry ops getdents to this function.

Definition at line 345 of file dentry.c.

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