[RFC/PATCH] Nonotify - A simplistic way to determine directory content changes
From: nf (nf2_at_scheinwelt.at)
Date: 05/31/04
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To: kernel mailing list <linux-kernel@vger.kernel.org> Date: Mon, 31 May 2004 15:43:40 +0200
Hi kernel experts,
After nagging about dnotify and unmount problems, i wrote my own little
patch and hope to provide a better solution.
My proposal is different from event based dnotify/inotify. Nonotify
provides an interface to make polling for directory changes more
efficient: Modification timestamps of files in a directory get stored in
an extra field of the directory inode. Therefore there is no need to
"stat" all the files in a directory for changes - a filemanager just has
to look at the "i_dcontents_mtime" timestamp of the directory.
The reason why i think that polling is better than sending events can be
easily demonstrated by running the following command in a directory
beeing watched by fam/dnotify:
$ time bash -c "for ((a=1;a<100000;a++)); do echo \"test $a\"; done >
test.txt"
with fam: 0:30.44elapsed 12%CPU (the rest goes to fam 45% and nautilus
40%)
without fam: 0:03.47elapsed 98%CPU
Dnotify slows down file operations by factor 10!!! I assume that all
event based mechanisms cause similar problems, because they generate
fireworks of events when a file is beeing written.
Nonotify has another advantage: It doesn't need to pin down inodes
(which would cause umount problems). When an inode object gets dropped
and reallocated by the kernel the "i_dcontents_mtime" field is
initialized to the current time. In this case an application watching a
directory will have to reread the directory although there were no
changes - but this will not happen very often (Because of the caching of
inode objects).
Please remember that this patch is only for testing. It works, but the
public interface for reading "i_dcontents_mtime" is not finished - i
have just reused the __unused fields of the "stat" structure. I think we
will need an extra system-call for this purpose, because changing the
"stat" structure would break C compatibility.
Please tell me what you think about this. I'm new to kernel programming
- i'm sure there are lots of things to improve.
Thanks,
Norbert
diff -ru linux-2.6.3-10mdk/fs/attr.c /usr/src/linux/fs/attr.c
--- linux-2.6.3-10mdk/fs/attr.c 2004-02-18 04:57:16.000000000 +0100
+++ /usr/src/linux/fs/attr.c 2004-05-31 13:26:40.000000000 +0200
@@ -11,6 +11,7 @@
#include <linux/string.h>
#include <linux/smp_lock.h>
#include <linux/dnotify.h>
+#include <linux/nonotify.h>
#include <linux/fcntl.h>
#include <linux/quotaops.h>
#include <linux/security.h>
@@ -184,8 +185,10 @@
}
if (!error) {
unsigned long dn_mask = setattr_mask(ia_valid);
- if (dn_mask)
+ if (dn_mask) {
dnotify_parent(dentry, dn_mask);
+ }
+ nonotify_parent(dentry);
}
return error;
}
diff -ru linux-2.6.3-10mdk/fs/inode.c /usr/src/linux/fs/inode.c
--- linux-2.6.3-10mdk/fs/inode.c 2004-04-19 18:54:32.000000000 +0200
+++ /usr/src/linux/fs/inode.c 2004-05-31 13:31:21.000000000 +0200
@@ -151,6 +151,9 @@
mapping->backing_dev_info = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
memset(&inode->u, 0, sizeof(inode->u));
inode->i_mapping = mapping;
+
+ /* Nonotify: Initially set dcontents_mtime to the current time. Why? When the inode object gets lost and reallocated, "clients" should reread the directory. */
+ inode->i_dcontents_mtime = current_kernel_time();
}
return inode;
}
diff -ru linux-2.6.3-10mdk/fs/Makefile /usr/src/linux/fs/Makefile
--- linux-2.6.3-10mdk/fs/Makefile 2004-04-19 18:54:32.000000000 +0200
+++ /usr/src/linux/fs/Makefile 2004-05-31 13:29:46.000000000 +0200
@@ -10,7 +10,7 @@
namei.o fcntl.o ioctl.o readdir.o select.o fifo.o locks.o \
dcache.o inode.o attr.o bad_inode.o file.o dnotify.o \
filesystems.o namespace.o seq_file.o xattr.o libfs.o \
- fs-writeback.o mpage.o direct-io.o aio.o
+ fs-writeback.o mpage.o direct-io.o aio.o nonotify.o
obj-$(CONFIG_EPOLL) += eventpoll.o
obj-$(CONFIG_COMPAT) += compat.o
diff -ru linux-2.6.3-10mdk/fs/read_write.c /usr/src/linux/fs/read_write.c
--- linux-2.6.3-10mdk/fs/read_write.c 2004-02-18 04:58:33.000000000 +0100
+++ /usr/src/linux/fs/read_write.c 2004-05-31 13:11:20.000000000 +0200
@@ -11,6 +11,7 @@
#include <linux/uio.h>
#include <linux/smp_lock.h>
#include <linux/dnotify.h>
+#include <linux/nonotify.h>
#include <linux/security.h>
#include <linux/module.h>
@@ -257,8 +258,10 @@
ret = file->f_op->write(file, buf, count, pos);
else
ret = do_sync_write(file, buf, count, pos);
- if (ret > 0)
+ if (ret > 0) {
dnotify_parent(file->f_dentry, DN_MODIFY);
+ nonotify_parent(file->f_dentry);
+ }
}
}
@@ -471,9 +474,11 @@
out:
if (iov != iovstack)
kfree(iov);
- if ((ret + (type == READ)) > 0)
+ if ((ret + (type == READ)) > 0) {
dnotify_parent(file->f_dentry,
(type == READ) ? DN_ACCESS : DN_MODIFY);
+ if (DN_MODIFY) nonotify_parent(file->f_dentry);
+ }
return ret;
}
diff -ru linux-2.6.3-10mdk/fs/stat.c /usr/src/linux/fs/stat.c
--- linux-2.6.3-10mdk/fs/stat.c 2004-02-18 04:57:17.000000000 +0100
+++ /usr/src/linux/fs/stat.c 2004-05-31 13:16:08.000000000 +0200
@@ -32,6 +32,7 @@
stat->size = i_size_read(inode);
stat->blocks = inode->i_blocks;
stat->blksize = inode->i_blksize;
+ stat->contents_mtime = inode->i_dcontents_mtime; /* Nonotify */
}
EXPORT_SYMBOL(generic_fillattr);
@@ -222,6 +223,17 @@
#endif
tmp.st_blocks = stat->blocks;
tmp.st_blksize = stat->blksize;
+
+ /* Nonotify hack: use unused structure members for contents_mtime
+ This is just for testing - We will need an extra system-call for
+ reading contents_mtime!
+ */
+
+ tmp.__unused4 = stat->contents_mtime.tv_sec;
+ tmp.__unused5 = stat->contents_mtime.tv_nsec;
+
+ /* end hack */
+
return copy_to_user(statbuf,&tmp,sizeof(tmp)) ? -EFAULT : 0;
}
diff -ru linux-2.6.3-10mdk/include/linux/fs.h /usr/src/linux/include/linux/fs.h
--- linux-2.6.3-10mdk/include/linux/fs.h 2004-04-19 18:54:32.000000000 +0200
+++ /usr/src/linux/include/linux/fs.h 2004-05-31 12:39:48.000000000 +0200
@@ -415,6 +415,8 @@
unsigned long i_dnotify_mask; /* Directory notify events */
struct dnotify_struct *i_dnotify; /* for directory notifications */
+ struct timespec i_dcontents_mtime; /* Nonotify: Time of last modification of a file in this directory or time this inode object has been allocated */
+
unsigned long i_state;
unsigned int i_flags;
diff -ru linux-2.6.3-10mdk/include/linux/stat.h /usr/src/linux/include/linux/stat.h
--- linux-2.6.3-10mdk/include/linux/stat.h 2004-02-18 04:57:24.000000000 +0100
+++ /usr/src/linux/include/linux/stat.h 2004-05-26 23:23:23.000000000 +0200
@@ -70,6 +70,7 @@
struct timespec ctime;
unsigned long blksize;
unsigned long blocks;
+ struct timespec contents_mtime;
};
#endif
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