Commit c23fbb6b authored by Eric Dumazet's avatar Eric Dumazet Committed by Linus Torvalds
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VFS: delay the dentry name generation on sockets and pipes 



1) Introduces a new method in 'struct dentry_operations'.  This method
   called d_dname() might be called from d_path() to build a pathname for
   special filesystems.  It is called without locks.

   Future patches (if we succeed in having one common dentry for all
   pipes/sockets) may need to change prototype of this method, but we now
   use : char *d_dname(struct dentry *dentry, char *buffer, int buflen);

2) Adds a dynamic_dname() helper function that eases d_dname() implementations

3) Defines d_dname method for sockets : No more sprintf() at socket
   creation.  This is delayed up to the moment someone does an access to
   /proc/pid/fd/...

4) Defines d_dname method for pipes : No more sprintf() at pipe
   creation.  This is delayed up to the moment someone does an access to
   /proc/pid/fd/...

A benchmark consisting of 1.000.000 calls to pipe()/close()/close() gives a
*nice* speedup on my Pentium(M) 1.6 Ghz :

3.090 s instead of 3.450 s

Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
Acked-by: default avatarChristoph Hellwig <hch@infradead.org>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 27932742

Documentation/filesystems/Locking

+2 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ prototypes: 
	int (*d_delete)(struct dentry *);

	void (*d_release)(struct dentry *);

	void (*d_iput)(struct dentry *, struct inode *);

	char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);



locking rules:

	none have BKL
@@ -25,6 +26,7 @@ d_compare: no yes no no 
d_delete:	yes		no		yes		no

d_release:	no		no		no		yes

d_iput:		no		no		no		yes

d_dname:	no		no		no		no



--------------------------- inode_operations --------------------------- 

prototypes:

Documentation/filesystems/vfs.txt

+22 −1
Original line number Diff line number Diff line
@@ -827,7 +827,7 @@ This describes how a filesystem can overload the standard dentry 
operations. Dentries and the dcache are the domain of the VFS and the

individual filesystem implementations. Device drivers have no business

here. These methods may be set to NULL, as they are either optional or

the VFS uses a default. As of kernel 2.6.13, the following members are

the VFS uses a default. As of kernel 2.6.22, the following members are

defined:



struct dentry_operations {
@@ -837,6 +837,7 @@ struct dentry_operations { 
	int (*d_delete)(struct dentry *);

	void (*d_release)(struct dentry *);

	void (*d_iput)(struct dentry *, struct inode *);

	char *(*d_dname)(struct dentry *, char *, int);

};



  d_revalidate: called when the VFS needs to revalidate a dentry. This
@@ -859,6 +860,26 @@ struct dentry_operations { 
	VFS calls iput(). If you define this method, you must call

	iput() yourself



  d_dname: called when the pathname of a dentry should be generated.

	Usefull for some pseudo filesystems (sockfs, pipefs, ...) to delay

	pathname generation. (Instead of doing it when dentry is created,

	its done only when the path is needed.). Real filesystems probably

	dont want to use it, because their dentries are present in global

	dcache hash, so their hash should be an invariant. As no lock is

	held, d_dname() should not try to modify the dentry itself, unless

	appropriate SMP safety is used. CAUTION : d_path() logic is quite

	tricky. The correct way to return for example "Hello" is to put it

	at the end of the buffer, and returns a pointer to the first char.

	dynamic_dname() helper function is provided to take care of this.



Example :



static char *pipefs_dname(struct dentry *dent, char *buffer, int buflen)

{

	return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",

				dentry->d_inode->i_ino);

}



Each dentry has a pointer to its parent dentry, as well as a hash list

of child dentries. Child dentries are basically like files in a

directory.

fs/dcache.c

+31 −0
Original line number Diff line number Diff line
@@ -1853,6 +1853,16 @@ char * d_path(struct dentry *dentry, struct vfsmount *vfsmnt, 
	struct vfsmount *rootmnt;

	struct dentry *root;



	/*

	 * We have various synthetic filesystems that never get mounted.  On

	 * these filesystems dentries are never used for lookup purposes, and

	 * thus don't need to be hashed.  They also don't need a name until a

	 * user wants to identify the object in /proc/pid/fd/.  The little hack

	 * below allows us to generate a name for these objects on demand:

	 */

	if (dentry->d_op && dentry->d_op->d_dname)

		return dentry->d_op->d_dname(dentry, buf, buflen);



	read_lock(&current->fs->lock);

	rootmnt = mntget(current->fs->rootmnt);

	root = dget(current->fs->root);
@@ -1865,6 +1875,27 @@ char * d_path(struct dentry *dentry, struct vfsmount *vfsmnt, 
	return res;

}



/*

 * Helper function for dentry_operations.d_dname() members

 */

char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,

			const char *fmt, ...)

{

	va_list args;

	char temp[64];

	int sz;



	va_start(args, fmt);

	sz = vsnprintf(temp, sizeof(temp), fmt, args) + 1;

	va_end(args);



	if (sz > sizeof(temp) || sz > buflen)

		return ERR_PTR(-ENAMETOOLONG);



	buffer += buflen - sz;

	return memcpy(buffer, temp, sz);

}



/*

 * NOTE! The user-level library version returns a

 * character pointer. The kernel system call just

fs/pipe.c

+12 −6
Original line number Diff line number Diff line
@@ -841,8 +841,18 @@ static int pipefs_delete_dentry(struct dentry *dentry) 
	return 0;

}



/*

 * pipefs_dname() is called from d_path().

 */

static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)

{

	return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",

				dentry->d_inode->i_ino);

}



static struct dentry_operations pipefs_dentry_operations = {

	.d_delete	= pipefs_delete_dentry,

	.d_dname	= pipefs_dname,

};



static struct inode * get_pipe_inode(void)
@@ -888,8 +898,7 @@ struct file *create_write_pipe(void) 
	struct inode *inode;

	struct file *f;

	struct dentry *dentry;

	char name[32];

	struct qstr this;

	struct qstr name = { .name = "" };



	f = get_empty_filp();

	if (!f)
@@ -899,11 +908,8 @@ struct file *create_write_pipe(void) 
	if (!inode)

		goto err_file;



	this.len = sprintf(name, "[%lu]", inode->i_ino);

	this.name = name;

	this.hash = 0;

	err = -ENOMEM;

	dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &this);

	dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &name);

	if (!dentry)

		goto err_inode;

include/linux/dcache.h

+6 −0
Original line number Diff line number Diff line
@@ -133,6 +133,7 @@ struct dentry_operations { 
	int (*d_delete)(struct dentry *);

	void (*d_release)(struct dentry *);

	void (*d_iput)(struct dentry *, struct inode *);

	char *(*d_dname)(struct dentry *, char *, int);

};



/* the dentry parameter passed to d_hash and d_compare is the parent
@@ -293,6 +294,11 @@ extern struct dentry * d_hash_and_lookup(struct dentry *, struct qstr *); 
/* validate "insecure" dentry pointer */

extern int d_validate(struct dentry *, struct dentry *);



/*

 * helper function for dentry_operations.d_dname() members

 */

extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);



extern char * d_path(struct dentry *, struct vfsmount *, char *, int);

  

/* Allocation counts.. */

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