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Subject[patch] explicit dcache <-> user-space cache coherency, sys_mark_dir_clean(), O_CLEAN

> What Samba needs is a way to tell between two points in time whether the
> directory contents have changed in any way - nothing more. Only one new
> syscall is used to maintain the Samba dcache:
>
> long sys_mark_dir_clean(dirfd);

> this is how Samba could create a file atomically:
>
> sys_create(name, mode | O_CLEAN);

i've attached a quick patch (against 2.6.3) that implements the new
sys_mark_dir_clean() syscall and O_CLEAN support in all open() variants,
just to have an idea of how it looks like roughly. (It's incomplete -
e.g. there's no explicit way to do an atomic unlink or rename.)

i've also attached dir-cache.c, a simple testcode for the new
functionality. It marks the current directory clean and tries to open
the "./1" file via O_CLEAN with 1 second delay. Start this in one shell
and do VFS-namespace modifying ops in another window (eg. "rm -f 2;
touch 2") and see the dir-cache code react to it - the 'clean' bit is
lost, and the file open-create does not succeed if the directory is not
clean.

there's a new dentry flag that is maintained under the directory's i_sem
semaphore. (It would be simpler to have the flag on the inode level,
that way the invalidation could be done as a simple filter to the
dnotify function.)

Ingo
--- linux/arch/i386/kernel/entry.S.orig
+++ linux/arch/i386/kernel/entry.S
@@ -882,5 +882,6 @@ ENTRY(sys_call_table)
.long sys_utimes
.long sys_fadvise64_64
.long sys_ni_syscall /* sys_vserver */
+ .long sys_mark_dir_clean

syscall_table_size=(.-sys_call_table)
--- linux/include/linux/dcache.h.orig
+++ linux/include/linux/dcache.h
@@ -153,9 +153,25 @@ d_iput: no no yes

#define DCACHE_REFERENCED 0x0008 /* Recently used, don't discard. */
#define DCACHE_UNHASHED 0x0010
+#define DCACHE_USER_CLEAN 0x0020 /* userspace cache coherent */

extern spinlock_t dcache_lock;

+static inline void d_user_flush(struct dentry *dentry)
+{
+ dentry->d_vfs_flags &= ~DCACHE_USER_CLEAN;
+}
+
+static inline void d_user_mark_clean(struct dentry *dentry)
+{
+ dentry->d_vfs_flags |= DCACHE_USER_CLEAN;
+}
+
+static inline long d_user_valid(struct dentry *dentry)
+{
+ return (dentry->d_vfs_flags & DCACHE_USER_CLEAN) != 0;
+}
+
/**
* d_drop - drop a dentry
* @dentry: dentry to drop
--- linux/include/asm-generic/errno.h.orig
+++ linux/include/asm-generic/errno.h
@@ -96,5 +96,6 @@

#define ENOMEDIUM 123 /* No medium found */
#define EMEDIUMTYPE 124 /* Wrong medium type */
+#define EFLUSH 125 /* cache not valid */

#endif
--- linux/include/asm-i386/fcntl.h.orig
+++ linux/include/asm-i386/fcntl.h
@@ -20,6 +20,7 @@
#define O_LARGEFILE 0100000
#define O_DIRECTORY 0200000 /* must be a directory */
#define O_NOFOLLOW 0400000 /* don't follow links */
+#define O_CLEAN 01000000 /* parent dir must be clean */

#define F_DUPFD 0 /* dup */
#define F_GETFD 1 /* get close_on_exec */
--- linux/fs/open.c.orig
+++ linux/fs/open.c
@@ -747,6 +747,7 @@ struct file *filp_open(const char * file
namei_flags++;
if (namei_flags & O_TRUNC)
namei_flags |= 2;
+ namei_flags |= flags & O_CLEAN;

error = open_namei(filename, namei_flags, mode, &nd);
if (!error)
@@ -1029,6 +1030,26 @@ out_unlock:

EXPORT_SYMBOL(sys_close);

+asmlinkage long sys_mark_dir_clean(unsigned int fd)
+{
+ struct file *filp;
+ long ret = -EBADF;
+
+ filp = fget(fd);
+ if (!filp)
+ return ret;
+
+ down(&filp->f_dentry->d_inode->i_sem);
+ ret = d_user_valid(filp->f_dentry);
+ d_user_mark_clean(filp->f_dentry);
+ up(&filp->f_dentry->d_inode->i_sem);
+
+ fput(filp);
+
+ return ret;
+}
+
+
/*
* This routine simulates a hangup on the tty, to arrange that users
* are given clean terminals at login time.
--- linux/fs/namei.c.orig
+++ linux/fs/namei.c
@@ -1295,11 +1295,23 @@ do_last:
goto exit;
}

+ /*
+ * Did user-space require the parent directory to be clean
+ * but it was invalid?:
+ */
+ error = -EFLUSH;
+ if ((flag & O_CLEAN) && !d_user_valid(dir)) {
+ up(&dir->d_inode->i_sem);
+ goto exit;
+ }
+
/* Negative dentry, just create the file */
if (!dentry->d_inode) {
if (!IS_POSIXACL(dir->d_inode))
mode &= ~current->fs->umask;
error = vfs_create(dir->d_inode, dentry, mode, nd);
+ if (!error)
+ d_user_flush(dir);
up(&dir->d_inode->i_sem);
dput(nd->dentry);
nd->dentry = dentry;
@@ -1493,6 +1505,8 @@ asmlinkage long sys_mknod(const char __u
}
dput(dentry);
}
+ if (!error)
+ d_user_flush(nd.dentry);
up(&nd.dentry->d_inode->i_sem);
path_release(&nd);
out:
@@ -1545,6 +1559,8 @@ asmlinkage long sys_mkdir(const char __u
if (!IS_POSIXACL(nd.dentry->d_inode))
mode &= ~current->fs->umask;
error = vfs_mkdir(nd.dentry->d_inode, dentry, mode);
+ if (!error)
+ d_user_flush(nd.dentry);
dput(dentry);
}
up(&nd.dentry->d_inode->i_sem);
@@ -1653,6 +1669,8 @@ asmlinkage long sys_rmdir(const char __u
error = PTR_ERR(dentry);
if (!IS_ERR(dentry)) {
error = vfs_rmdir(nd.dentry->d_inode, dentry);
+ if (!error)
+ d_user_flush(nd.dentry);
dput(dentry);
}
up(&nd.dentry->d_inode->i_sem);
@@ -1728,6 +1746,8 @@ asmlinkage long sys_unlink(const char __
if (inode)
atomic_inc(&inode->i_count);
error = vfs_unlink(nd.dentry->d_inode, dentry);
+ if (!error)
+ d_user_flush(nd.dentry);
exit2:
dput(dentry);
}
@@ -2099,6 +2119,10 @@ static inline int do_rename(const char *

error = vfs_rename(old_dir->d_inode, old_dentry,
new_dir->d_inode, new_dentry);
+ if (!error) {
+ d_user_flush(old_dir);
+ d_user_flush(new_dir);
+ }
exit5:
dput(new_dentry);
exit4:/*
* Copyright (C) Ingo Molnar, 2002
*/
#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/times.h>
#include <sys/wait.h>
#include <sys/ioctl.h>
#include <linux/unistd.h>
#define __NR_sys_mark_dir_clean 274
_syscall1(int, sys_mark_dir_clean, int, fd);

#define O_DIRECTORY 0200000 /* must be a directory */
#define O_CLEAN 01000000 /* parent dir must be clean */
int main(int argc, char **argv)
{
int fd, fd2, clean;
fd = open(".", O_RDONLY | O_DIRECTORY);
if (fd <= 0) {
perror("fd:");
exit(-1);
}
for (;;) {
clean = sys_mark_dir_clean(fd);
printf("clean:%d ", clean); fflush(stdout);
sleep(1);
fd2 = open("./1", O_CREAT|O_TRUNC|O_CLEAN, 0777);
close(fd2);
printf("fd:%d\n", fd2);
sleep(1);
}
return 0;
}
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