linux-kernel - Re: [RFC v3][PATCH 7/9] Infrastructure for shared objects

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Date:	Thu, 4 Sep 2008 11:38:03 +0200
From:	Louis Rilling <Louis.Rilling@...labs.com>
To:	Oren Laadan <orenl@...columbia.edu>
Cc:	dave@...ux.vnet.ibm.com, arnd@...db.de, jeremy@...p.org,
	linux-kernel@...r.kernel.org, containers@...ts.linux-foundation.org
Subject: Re: [RFC v3][PATCH 7/9] Infrastructure for shared objects

On Thu, Sep 04, 2008 at 04:05:22AM -0400, Oren Laadan wrote:
>
> Infrastructure to handle objects that may be shared and referenced by
> multiple tasks or other objects, e..g open files, memory address space
> etc.
>
> The state of shared objects is saved once. On the first encounter, the
> state is dumped and the object is assigned a unique identifier and also
> stored in a hash table (indexed by its physical kenrel address). From
> then on the object will be found in the hash and only its identifier is
> saved.
>
> On restart the identifier is looked up in the hash table; if not found
> then the state is read, the object is created, and added to the hash
> table (this time indexed by its identifier). Otherwise, the object in
> the hash table is used.
>

[...]

> diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
> new file mode 100644
> index 0000000..442b08c
> --- /dev/null
> +++ b/checkpoint/objhash.c
> @@ -0,0 +1,205 @@
> +/*
> + *  Checkpoint-restart - object hash infrastructure to manage shared objects
> + *
> + *  Copyright (C) 2008 Oren Laadan
> + *
> + *  This file is subject to the terms and conditions of the GNU General Public
> + *  License.  See the file COPYING in the main directory of the Linux
> + *  distribution for more details.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/file.h>
> +#include <linux/hash.h>
> +#include <linux/ckpt.h>
> +
> +struct cr_objref {
> +	int objref;
> +	void *ptr;
> +	unsigned short type;
> +	unsigned short flags;
> +	struct hlist_node hash;
> +};
> +
> +struct cr_objhash {
> +	struct hlist_head *head;
> +	int objref_index;
> +};
> +
> +#define CR_OBJHASH_NBITS  10
> +#define CR_OBJHASH_TOTAL  (1UL << CR_OBJHASH_NBITS - 1)

Why -1? This makes a total number of 512 entries, which will break below with
hashes in range 0..1023.

> +
> +static void cr_obj_ref_drop(struct cr_objref *obj)
> +{
> +	switch (obj->type) {
> +	case CR_OBJ_FILE:
> +		fput((struct file *) obj->ptr);
> +		break;
> +	default:
> +		BUG();
> +	}
> +}
> +
> +static void cr_obj_ref_grab(struct cr_objref *obj)
> +{
> +	switch (obj->type) {
> +	case CR_OBJ_FILE:
> +		get_file((struct file *) obj->ptr);
> +		break;
> +	default:
> +		BUG();
> +	}
> +}
> +
> +static void cr_objhash_clear(struct cr_objhash *objhash)
> +{
> +	struct hlist_head *h = objhash->head;
> +	struct hlist_node *n, *t;
> +	struct cr_objref *obj;
> +	int i;
> +
> +	for (i = 0; i < CR_OBJHASH_TOTAL; i++) {
> +		hlist_for_each_entry_safe(obj, n, t, &h[i], hash) {
> +			cr_obj_ref_drop(obj);
> +			kfree(obj);
> +		}
> +	}
> +}
> +
> +void cr_objhash_free(struct cr_ctx *ctx)
> +{
> +	struct cr_objhash *objhash = ctx->objhash;
> +
> +	if (objhash) {
> +		cr_objhash_clear(objhash);
> +		kfree(objhash->head);
> +		kfree(ctx->objhash);
> +		ctx->objhash = NULL;
> +	}
> +}
> +
> +int cr_objhash_alloc(struct cr_ctx *ctx)
> +{
> +	struct cr_objhash *objhash;
> +	struct hlist_head *head;
> +
> +	objhash = kzalloc(sizeof(*objhash), GFP_KERNEL);
> +	if (!objhash)
> +		return -ENOMEM;
> +	head = kzalloc(CR_OBJHASH_TOTAL * sizeof(*head), GFP_KERNEL);

512 entries allocated

> +	if (!head) {
> +		kfree(objhash);
> +		return -ENOMEM;
> +	}
> +
> +	objhash->head = head;
> +	objhash->objref_index = 1;
> +
> +	ctx->objhash = objhash;
> +	return 0;
> +}
> +
> +static struct cr_objref *cr_obj_find_by_ptr(struct cr_ctx *ctx, void *ptr)
> +{
> +	struct hlist_head *h;
> +	struct hlist_node *n;
> +	struct cr_objref *obj;
> +
> +	h = &ctx->objhash->head[hash_ptr(ptr, CR_OBJHASH_NBITS)];

access to entries 0..1023

Louis

-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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