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Subject[PATCH 1/3] sysfs representation of stacked devices (common) (rev.2)
This patch adds bd_claim_by_kobject and bd_release_from_kobject
which create/remove symlinks between the claimed bdev and
the holder.

--
Jun'ichi Nomura, NEC Solutions (America), Inc.
Adding bd_claim_by_kobject/bd_release_from_kobject for use by
stacked device drivers (dm and md)

Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>

--- linux-2.6.15/include/linux/fs.h 2006-01-02 22:21:10.000000000 -0500
+++ linux-2.6.15/include/linux/fs.h 2006-02-21 19:04:46.000000000 -0500
@@ -373,6 +373,8 @@ struct block_device {
struct list_head bd_inodes;
void * bd_holder;
int bd_holders;
+ struct kobject bd_holder_dir;
+ struct list_head bd_holder_list;
struct block_device * bd_contains;
unsigned bd_block_size;
struct hd_struct * bd_part;
@@ -1351,6 +1353,8 @@ extern int blkdev_get(struct block_devic
extern int blkdev_put(struct block_device *);
extern int bd_claim(struct block_device *, void *);
extern void bd_release(struct block_device *);
+extern int bd_claim_by_kobject(struct block_device *, void *, struct kobject *);
+extern void bd_release_from_kobject(struct block_device *, struct kobject *);

/* fs/char_dev.c */
extern int alloc_chrdev_region(dev_t *, unsigned, unsigned, const char *);
--- linux-2.6.15/include/linux/genhd.h 2006-01-02 22:21:10.000000000 -0500
+++ linux-2.6.15/include/linux/genhd.h 2006-02-21 11:38:01.000000000 -0500
@@ -114,6 +114,7 @@ struct gendisk {
int number; /* more of the same */
struct device *driverfs_dev;
struct kobject kobj;
+ struct kobject slave_dir;

struct timer_rand_state *random;
int policy;
--- linux-2.6.15/fs/block_dev.c 2006-01-02 22:21:10.000000000 -0500
+++ linux-2.6.15/fs/block_dev.c 2006-02-22 09:48:37.000000000 -0500
@@ -443,7 +443,159 @@ void bd_forget(struct inode *inode)
spin_unlock(&bdev_lock);
}

-int bd_claim(struct block_device *bdev, void *holder)
+/*
+ * Functions for bd_claim_by_kobject / bd_release_from_kobject
+ *
+ * If a kobject is passed to bd_claim_by_kobject()
+ * and the kobject has a parent directory,
+ * following symlinks are created:
+ * o from the kobject to the claimed bdev
+ * o from "holders" directory of the bdev to the parent of the kobject
+ * bd_release_from_kobject() removes these symlinks.
+ *
+ * Example:
+ * If /dev/dm-0 maps to /dev/sda, kobject corresponding to
+ * /sys/block/dm-0/slaves is passed to bd_claim_by_kobject(), then:
+ * /sys/block/dm-0/slaves/sda --> /sys/block/sda
+ * /sys/block/sda/holders/dm-0 --> /sys/block/dm-0
+ */
+
+static inline struct kobject * bdev_get_kobj(struct block_device *bdev)
+{
+ if (!bdev)
+ return NULL;
+ else if (bdev->bd_contains != bdev)
+ return kobject_get(&bdev->bd_part->kobj);
+ else
+ return kobject_get(&bdev->bd_disk->kobj);
+}
+
+static inline void add_symlink(struct kobject *from, struct kobject *to)
+{
+ if (!from || !to)
+ return;
+ sysfs_create_link(from, to, kobject_name(to));
+}
+
+static inline void del_symlink(struct kobject *from, struct kobject *to)
+{
+ if (!from || !to)
+ return;
+ sysfs_remove_link(from, kobject_name(to));
+}
+
+static void link_bd_holder(struct block_device *bdev, struct kobject *holder)
+{
+ struct kobject *kobj;
+
+ if (!holder->parent)
+ return;
+
+ kobj = bdev_get_kobj(bdev);
+ add_symlink(holder, kobj);
+ add_symlink(&bdev->bd_holder_dir, holder->parent);
+ kobject_put(kobj);
+}
+
+static void unlink_bd_holder(struct block_device *bdev, struct kobject *holder)
+{
+ struct kobject *kobj;
+
+ if (!holder->parent)
+ return;
+
+ kobj = bdev_get_kobj(bdev);
+ del_symlink(holder, kobj);
+ del_symlink(&bdev->bd_holder_dir, holder->parent);
+ kobject_put(kobj);
+}
+
+/* This is a mere directory in sysfs. No methods are needed. */
+static struct kobj_type bd_holder_ktype = {
+ .release = NULL,
+ .sysfs_ops = NULL,
+ .default_attrs = NULL,
+};
+
+static inline void add_holder_dir(struct block_device *bdev)
+{
+ struct kobject *kobj = &bdev->bd_holder_dir;
+
+ kobj->ktype = &bd_holder_ktype;
+ kobject_set_name(kobj, "holders");
+ kobj->parent = bdev_get_kobj(bdev);
+ kobject_init(kobj);
+ kobject_add(kobj);
+ kobject_put(kobj->parent);
+}
+
+static inline void del_holder_dir(struct block_device *bdev)
+{
+ /*
+ * Don't kobject_unregister to avoid memory allocation
+ * in kobject_hotplug.
+ */
+ kobject_del(&bdev->bd_holder_dir);
+ kobject_put(&bdev->bd_holder_dir);
+}
+
+/* bd_holder_list is protected by bdev_lock */
+struct bd_holder {
+ struct list_head list; /* chain of holders of the bdev */
+ int count; /* references from the holder */
+ struct kobject *kobj; /* holder kobject */
+};
+
+static int add_bd_holder(struct block_device *bdev, struct kobject *kobj)
+{
+ struct bd_holder *bo;
+
+ list_for_each_entry(bo, &bdev->bd_holder_list, list) {
+ if (bo->kobj == kobj) {
+ bo->count++;
+ return 0;
+ }
+ }
+
+ if (list_empty(&bdev->bd_holder_list))
+ add_holder_dir(bdev);
+
+ bo = kmalloc(sizeof(*bo), GFP_KERNEL);
+ if (!bo)
+ return -ENOMEM;
+
+ bo->count = 1;
+ bo->kobj = kobj;
+ list_add_tail(&bo->list, &bdev->bd_holder_list);
+ link_bd_holder(bdev, kobj);
+
+ return 0;
+}
+
+static int del_bd_holder(struct block_device *bdev, struct kobject *kobj)
+{
+ struct bd_holder *bo;
+
+ list_for_each_entry(bo, &bdev->bd_holder_list, list) {
+ if (bo->kobj == kobj) {
+ bo->count--;
+ BUG_ON(bo->count < 0);
+ if (!bo->count) {
+ unlink_bd_holder(bdev, kobj);
+ list_del(&bo->list);
+ kfree(bo);
+ }
+ break;
+ }
+ }
+
+ if (list_empty(&bdev->bd_holder_list))
+ del_holder_dir(bdev);
+
+ return 0;
+}
+
+int bd_claim_by_kobject(struct block_device *bdev, void *holder, struct kobject *kobj)
{
int res;
spin_lock(&bdev_lock);
@@ -464,6 +616,9 @@ int bd_claim(struct block_device *bdev,
res = 0; /* is a partition of an un-held device */

/* now impose change */
+ if (res == 0 && kobj)
+ res = add_bd_holder(bdev, kobj);
+
if (res==0) {
/* note that for a whole device bd_holders
* will be incremented twice, and bd_holder will
@@ -478,11 +633,20 @@ int bd_claim(struct block_device *bdev,
return res;
}

+EXPORT_SYMBOL(bd_claim_by_kobject);
+
+int bd_claim(struct block_device *bdev, void *holder)
+{
+ return bd_claim_by_kobject(bdev, holder, NULL);
+}
+
EXPORT_SYMBOL(bd_claim);

-void bd_release(struct block_device *bdev)
+void bd_release_from_kobject(struct block_device *bdev, struct kobject *kobj)
{
spin_lock(&bdev_lock);
+ if (kobj)
+ del_bd_holder(bdev, kobj);
if (!--bdev->bd_contains->bd_holders)
bdev->bd_contains->bd_holder = NULL;
if (!--bdev->bd_holders)
@@ -490,6 +654,13 @@ void bd_release(struct block_device *bde
spin_unlock(&bdev_lock);
}

+EXPORT_SYMBOL(bd_release_from_kobject);
+
+void bd_release(struct block_device *bdev)
+{
+ bd_release_from_kobject(bdev, NULL);
+}
+
EXPORT_SYMBOL(bd_release);

/*
@@ -578,6 +749,7 @@ static int do_open(struct block_device *
if (!bdev->bd_openers) {
bdev->bd_disk = disk;
bdev->bd_contains = bdev;
+ INIT_LIST_HEAD(&bdev->bd_holder_list);
if (!part) {
struct backing_dev_info *bdi;
if (disk->fops->open) {
--- linux-2.6.15/fs/partitions/check.c 2006-01-02 22:21:10.000000000 -0500
+++ linux-2.6.15/fs/partitions/check.c 2006-02-21 14:30:23.000000000 -0500
@@ -293,6 +293,13 @@ struct kobj_type ktype_part = {
.sysfs_ops = &part_sysfs_ops,
};

+/* This is a mere directory in sysfs. No methods are needed. */
+static struct kobj_type slave_ktype = {
+ .release = NULL,
+ .sysfs_ops = NULL,
+ .default_attrs = NULL,
+};
+
void delete_partition(struct gendisk *disk, int part)
{
struct hd_struct *p = disk->part[part-1];
@@ -343,6 +350,12 @@ static void disk_sysfs_symlinks(struct g
sysfs_create_link(&disk->kobj,&target->kobj,"device");
sysfs_create_link(&target->kobj,&disk->kobj,"block");
}
+
+ /* create subdirectory for symlinks to underlying device */
+ disk->slave_dir.ktype = &slave_ktype;
+ kobject_set_name(&disk->slave_dir, "slaves");
+ disk->slave_dir.parent = &disk->kobj;
+ kobject_register(&disk->slave_dir);
}

/* Not exported, helper to add_disk(). */
@@ -460,6 +473,7 @@ void del_gendisk(struct gendisk *disk)

devfs_remove_disk(disk);

+ kobject_unregister(&disk->slave_dir);
if (disk->driverfs_dev) {
sysfs_remove_link(&disk->kobj, "device");
sysfs_remove_link(&disk->driverfs_dev->kobj, "block");
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