[CFT][PATCH] lazy allocation of struct block_device

* [CFT][PATCH] lazy allocation of struct block_device
@ 2001-09-16 22:06 Alexander Viro
  2001-09-17 17:23 ` [CFT][PATCH] (2.4.10-pre10) " Alexander Viro
  0 siblings, 1 reply; 2+ messages in thread
From: Alexander Viro @ 2001-09-16 22:06 UTC (permalink / raw)
  To: linux-kernel; +Cc: Linus Torvalds

	Folks, patch below changes the allocation rules for
struct block_device.

	Summary:
* init_special_inode() doesn't set ->i_bdev anymore.
* bd_acquire(inode) finds/allocates block_device, grabs a reference to it
  and sets ->i_bdev if needed.  It also inserts inode into bdev->bd_inodes.
* ->i_bdev doesn't contribute to refcount
* when refcount on block_device hits zero we go through all inodes still on
  ->bd_inodes and reset their ->i_bdev (and remove them from the list).
* we do bd_acquire() upon open, mount, etc.
* we do bdput(inode->i_bdev) on blkdev_put(), blkdev_close(), etc.
* when struct inode is freed we remove it from ->i_bdev->bd_inodes (if
  ->i_bdev is non-NULL, that is)
* if blkdev_open() fails it does bdput() (normal sequence is bd_acquire(inode);
  blkdev_open(inode->i_bdev); - that way we don't have to mess with bdput()
  if open fails).

IOW, block_device is kept around only when we need it. Notice that if
filesystem wants to associate block_device with inode from the very
beginning it can just set ->i_bdev when inode is created and do bdput()
in ->clear_inode(). bd_acquire() will see non-NULL ->i_bdev and just
bump the refcount, so everything works nicely both for normal device
nodes and for devfs-style setups.

Code review and help with testing are welcome.  It seems to be working here
and it's small enough to have a chance of being correct, but it needs more
testing before it can be considered for inclusion.  Linus, if you have
problems with design - please tell.
							Cheers,
								Al

diff -urN S10-pre9/drivers/block/rd.c S10-pre9-bdev/drivers/block/rd.c

--- S10-pre9/drivers/block/rd.c	Fri Sep 14 12:58:43 2001
+++ S10-pre9-bdev/drivers/block/rd.c	Sat Sep 15 02:02:57 2001
@@ -374,10 +374,8 @@
 	for (i = 0 ; i < NUM_RAMDISKS; i++) {
 		struct block_device *bdev = rd_bdev[i];
 		rd_bdev[i] = NULL;
-		if (bdev) {
+		if (bdev)
 			blkdev_put(bdev, BDEV_FILE);
-			bdput(bdev);
-		}
 		destroy_buffers(MKDEV(MAJOR_NR, i));
 	}
 
diff -urN S10-pre9/drivers/char/raw.c S10-pre9-bdev/drivers/char/raw.c
--- S10-pre9/drivers/char/raw.c	Tue Jul  3 21:09:09 2001
+++ S10-pre9-bdev/drivers/char/raw.c	Sat Sep 15 02:00:50 2001
@@ -100,6 +100,7 @@
 		goto out;
 
 	rdev = to_kdev_t(bdev->bd_dev);
+	atomic_inc(&bdev->bd_count);
 	err = blkdev_get(bdev, filp->f_mode, 0, BDEV_RAW);
 	if (err)
 		goto out;
diff -urN S10-pre9/drivers/md/md.c S10-pre9-bdev/drivers/md/md.c
--- S10-pre9/drivers/md/md.c	Fri Sep 14 12:58:44 2001
+++ S10-pre9-bdev/drivers/md/md.c	Sat Sep 15 02:00:50 2001
@@ -653,11 +653,10 @@
 
 static void unlock_rdev (mdk_rdev_t *rdev)
 {
-	if (!rdev->bdev)
+	struct block_device *bdev = rdev->bdev;
+	if (!bdev)
 		MD_BUG();
-	blkdev_put(rdev->bdev, BDEV_FILE);
-	bdput(rdev->bdev);
-	rdev->bdev = NULL;
+	blkdev_put(bdev, BDEV_FILE);
 }
 
 void md_autodetect_dev (kdev_t dev);
diff -urN S10-pre9/fs/block_dev.c S10-pre9-bdev/fs/block_dev.c
--- S10-pre9/fs/block_dev.c	Fri Sep 14 12:58:45 2001
+++ S10-pre9-bdev/fs/block_dev.c	Sat Sep 15 05:51:58 2001
@@ -389,6 +389,7 @@
 	{
 		memset(bdev, 0, sizeof(*bdev));
 		sema_init(&bdev->bd_sem, 1);
+		INIT_LIST_HEAD(&bdev->bd_inodes);
 	}
 }
 
@@ -466,16 +467,57 @@
 
 void bdput(struct block_device *bdev)
 {
-	if (atomic_dec_and_test(&bdev->bd_count)) {
-		spin_lock(&bdev_lock);
+	if (atomic_dec_and_lock(&bdev->bd_count, &bdev_lock)) {
+		struct list_head *p;
 		if (atomic_read(&bdev->bd_openers))
 			BUG();
 		list_del(&bdev->bd_hash);
+		while ( (p = bdev->bd_inodes.next) != &bdev->bd_inodes ) {
+			struct inode *inode;
+			inode = list_entry(p, struct inode, i_devices);
+			list_del(p);
+			inode->i_bdev = NULL;
+		}
 		spin_unlock(&bdev_lock);
 		destroy_bdev(bdev);
 	}
 }
 
+int bd_acquire(struct inode *inode)
+{
+	struct block_device *bdev;
+	spin_lock(&bdev_lock);
+	if (inode->i_bdev) {
+		atomic_inc(&inode->i_bdev->bd_count);
+		spin_unlock(&bdev_lock);
+		return 0;
+	}
+	spin_unlock(&bdev_lock);
+	bdev = bdget(kdev_t_to_nr(inode->i_rdev));
+	if (!bdev)
+		return -ENOMEM;
+	spin_lock(&bdev_lock);
+	if (!inode->i_bdev) {
+		inode->i_bdev = bdev;
+		list_add(&inode->i_devices, &bdev->bd_inodes);
+	} else if (inode->i_bdev != bdev)
+		BUG();
+	spin_unlock(&bdev_lock);
+	return 0;
+}
+
+/* Call when you free inode */
+
+void bd_forget(struct inode *inode)
+{
+	spin_lock(&bdev_lock);
+	if (inode->i_bdev) {
+		list_del(&inode->i_devices);
+		inode->i_bdev = NULL;
+	}
+	spin_unlock(&bdev_lock);
+}
+
 static struct {
 	const char *name;
 	struct block_device_operations *bdops;
@@ -646,13 +688,17 @@
 		}
 	}
 	up(&bdev->bd_sem);
+	if (ret)
+		bdput(bdev);
 	return ret;
 }
 
 int blkdev_open(struct inode * inode, struct file * filp)
 {
 	int ret = -ENXIO;
-	struct block_device *bdev = inode->i_bdev;
+	struct block_device *bdev;
+	bd_acquire(inode);
+	bdev = inode->i_bdev;
 	down(&bdev->bd_sem);
 	lock_kernel();
 	if (!bdev->bd_op)
@@ -668,6 +714,8 @@
 	}	
 	unlock_kernel();
 	up(&bdev->bd_sem);
+	if (ret)
+		bdput(bdev);
 	return ret;
 }	
 
@@ -700,6 +748,7 @@
 					/* kind to stay around. */
 	unlock_kernel();
 	up(&bdev->bd_sem);
+	bdput(bdev);
 	return ret;
 }
 
diff -urN S10-pre9/fs/devfs/base.c S10-pre9-bdev/fs/devfs/base.c
--- S10-pre9/fs/devfs/base.c	Sun Jul 29 01:54:47 2001
+++ S10-pre9-bdev/fs/devfs/base.c	Sat Sep 15 02:00:50 2001
@@ -2247,6 +2247,12 @@
 static struct file_operations devfs_dir_fops;
 static struct inode_operations devfs_symlink_iops;
 
+static void devfs_clear_inode (struct inode *inode)
+{
+	if (S_ISBLK(inode->i_mode))
+		bdput(inode->i_bdev);
+}
+
 static void devfs_read_inode (struct inode *inode)
 {
     struct devfs_entry *de;
@@ -2278,8 +2284,7 @@
     {
 	inode->i_rdev = MKDEV (de->u.fcb.u.device.major,
 			       de->u.fcb.u.device.minor);
-	inode->i_bdev = bdget (kdev_t_to_nr(inode->i_rdev));
-	if (inode->i_bdev)
+	if (bd_acquire(inode) == 0)
 	{
 	    if (!inode->i_bdev->bd_op && de->u.fcb.ops)
 		inode->i_bdev->bd_op = de->u.fcb.ops;
@@ -2383,6 +2388,7 @@
 { 
     read_inode:    devfs_read_inode,
     write_inode:   devfs_write_inode,
+    clear_inode:   devfs_clear_inode,
     statfs:        devfs_statfs,
 };
 
diff -urN S10-pre9/fs/devices.c S10-pre9-bdev/fs/devices.c
--- S10-pre9/fs/devices.c	Thu May 24 18:26:44 2001
+++ S10-pre9-bdev/fs/devices.c	Sat Sep 15 02:00:50 2001
@@ -207,7 +207,6 @@
 	} else if (S_ISBLK(mode)) {
 		inode->i_fop = &def_blk_fops;
 		inode->i_rdev = to_kdev_t(rdev);
-		inode->i_bdev = bdget(rdev);
 	} else if (S_ISFIFO(mode))
 		inode->i_fop = &def_fifo_fops;
 	else if (S_ISSOCK(mode))
diff -urN S10-pre9/fs/inode.c S10-pre9-bdev/fs/inode.c
--- S10-pre9/fs/inode.c	Fri Sep 14 12:58:45 2001
+++ S10-pre9-bdev/fs/inode.c	Sat Sep 15 02:00:50 2001
@@ -516,11 +516,9 @@
 	DQUOT_DROP(inode);
 	if (inode->i_sb && inode->i_sb->s_op && inode->i_sb->s_op->clear_inode)
 		inode->i_sb->s_op->clear_inode(inode);
-	if (inode->i_bdev) {
-		bdput(inode->i_bdev);
-		inode->i_bdev = NULL;
-	}
-	if (inode->i_cdev) {
+	if (inode->i_bdev)
+		bd_forget(inode);
+	else if (inode->i_cdev) {
 		cdput(inode->i_cdev);
 		inode->i_cdev = NULL;
 	}
@@ -778,6 +776,7 @@
 	inode->i_size = 0;
 	inode->i_generation = 0;
 	memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
+	INIT_LIST_HEAD(&inode->i_devices);
 	inode->i_pipe = NULL;
 	inode->i_bdev = NULL;
 	inode->i_cdev = NULL;
diff -urN S10-pre9/fs/partitions/ibm.c S10-pre9-bdev/fs/partitions/ibm.c
--- S10-pre9/fs/partitions/ibm.c	Fri Sep 14 12:58:45 2001
+++ S10-pre9-bdev/fs/partitions/ibm.c	Sat Sep 15 02:00:50 2001
@@ -47,9 +47,10 @@
 {
 	struct block_device *bdev = bdget(kdev_t_to_nr(kdev));
 	int rc = blkdev_get(bdev, 0, 1, BDEV_FILE);
-        if ( rc == 0 )
+        if ( rc == 0 ) {
 		rc = ioctl_by_bdev(bdev, HDIO_GETGEO, (unsigned long)geo);
-	blkdev_put(bdev,BDEV_FILE);
+		blkdev_put(bdev,BDEV_FILE);
+	}
 	return rc;
 }
 
@@ -58,9 +59,10 @@
 {
 	struct block_device *bdev = bdget(kdev_t_to_nr(kdev));
 	int rc = blkdev_get(bdev, 0, 1, BDEV_FILE);
-        if ( rc == 0 )
+        if ( rc == 0 ) {
 		rc = ioctl_by_bdev(bdev, BIODASDINFO, (unsigned long)(info));
-	blkdev_put(bdev,BDEV_FILE);
+		blkdev_put(bdev,BDEV_FILE);
+	}
 	return rc;
 }
 
diff -urN S10-pre9/fs/super.c S10-pre9-bdev/fs/super.c
--- S10-pre9/fs/super.c	Fri Sep 14 12:58:45 2001
+++ S10-pre9-bdev/fs/super.c	Sat Sep 15 02:00:50 2001
@@ -925,6 +925,7 @@
 	error = -EACCES;
 	if (nd.mnt->mnt_flags & MNT_NODEV)
 		goto out;
+	bd_acquire(inode);
 	bdev = inode->i_bdev;
 	bdops = devfs_get_ops ( devfs_get_handle_from_inode (inode) );
 	if (bdops) bdev->bd_op = bdops;
@@ -982,8 +983,6 @@
 	if (!fs_type->read_super(s, data, 0))
 		goto out_fail;
 	unlock_super(s);
-	/* tell bdcache that we are going to keep this one */
-	atomic_inc(&bdev->bd_count);
 	get_filesystem(fs_type);
 	path_release(&nd);
 	return s;
@@ -1128,10 +1127,9 @@
 	sb->s_type = NULL;
 	unlock_super(sb);
 	unlock_kernel();
-	if (bdev) {
+	if (bdev)
 		blkdev_put(bdev, BDEV_FS);
-		bdput(bdev);
-	} else
+	else
 		put_unnamed_dev(dev);
 	spin_lock(&sb_lock);
 	list_del(&sb->s_list);
@@ -1718,6 +1716,7 @@
 	if (!ROOT_DEV)
 		panic("I have no root and I want to scream");
 
+retry:
 	bdev = bdget(kdev_t_to_nr(ROOT_DEV));
 	if (!bdev)
 		panic(__FUNCTION__ ": unable to allocate root device");
@@ -1729,7 +1728,7 @@
 	retval = blkdev_get(bdev, mode, 0, BDEV_FS);
 	if (retval == -EROFS) {
 		root_mountflags |= MS_RDONLY;
-		retval = blkdev_get(bdev, FMODE_READ, 0, BDEV_FS);
+		goto retry;
 	}
 	if (retval) {
 	        /*
@@ -1977,6 +1976,7 @@
 		int blivet;
 		struct block_device *ramdisk = old_rootmnt->mnt_sb->s_bdev;
 
+		atomic_inc(&ramdisk->bd_count);
 		blivet = blkdev_get(ramdisk, FMODE_READ, 0, BDEV_FS);
 		printk(KERN_NOTICE "Trying to unmount old root ... ");
 		if (!blivet) {
diff -urN S10-pre9/include/linux/fs.h S10-pre9-bdev/include/linux/fs.h
--- S10-pre9/include/linux/fs.h	Fri Sep 14 12:58:46 2001
+++ S10-pre9-bdev/include/linux/fs.h	Sat Sep 15 02:00:50 2001
@@ -404,6 +404,7 @@
 	atomic_t		bd_openers;
 	const struct block_device_operations *bd_op;
 	struct semaphore	bd_sem;	/* open/close mutex */
+	struct list_head	bd_inodes;
 };
 
 struct inode {
@@ -438,6 +439,7 @@
 	struct address_space	*i_mapping;
 	struct address_space	i_data;	
 	struct dquot		*i_dquot[MAXQUOTAS];
+	struct list_head	i_devices;
 	/* These three should probably be a union */
 	struct pipe_inode_info	*i_pipe;
 	struct block_device	*i_bdev;
@@ -1026,6 +1028,8 @@
 extern int register_blkdev(unsigned int, const char *, struct block_device_operations *);
 extern int unregister_blkdev(unsigned int, const char *);
 extern struct block_device *bdget(dev_t);
+extern int bd_acquire(struct inode *inode);
+extern void bd_forget(struct inode *inode);
 extern void bdput(struct block_device *);
 extern struct char_device *cdget(dev_t);
 extern void cdput(struct char_device *);
diff -urN S10-pre9/mm/swapfile.c S10-pre9-bdev/mm/swapfile.c
--- S10-pre9/mm/swapfile.c	Fri Sep 14 12:58:46 2001
+++ S10-pre9-bdev/mm/swapfile.c	Sat Sep 15 02:00:50 2001
@@ -764,6 +764,7 @@
 		p->swap_device = dev;
 		set_blocksize(dev, PAGE_SIZE);
 		
+		bd_acquire(swap_inode);
 		bdev = swap_inode->i_bdev;
 		bdops = devfs_get_ops(devfs_get_handle_from_inode(swap_inode));
 		if (bdops) bdev->bd_op = bdops;


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