Messages in this thread Patch in this message | | | Subject | Re: [RFC v5][PATCH 7/8] Infrastructure for shared objects | From | Dave Hansen <> | Date | Tue, 16 Sep 2008 09:48:19 -0700 |
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On Sat, 2008-09-13 at 19:06 -0400, Oren Laadan wrote: > +=== Shared resources (objects) > + > +Many resources used by tasks may be shared by more than one task (e.g. > +file descriptors, memory address space, etc), or even have multiple > +references from other resources (e.g. a single inode that represents > +two ends of a pipe). > + > +Clearly, the state of shared objects need only be saved once, even if > +they occur multiple times. We use a hash table (ctx->objhash) to keep > +track of shared objects in the following manner. > + > +On the first encounter, the state is dumped and the object is assigned > +a unique identifier and also stored in the 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.
kernel? ^^^^^^
> +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. > + > +The interface for the hash table is the following: > + > +cr_obj_get_by_ptr - find the unique identifier - object reference (objref) > + of the object that is pointer to by ptr (or 0 if not found) [checkpoint] > + > +cr_obj_add_ptr - add the object pointed to by ptr to the hash table if > + it isn't already there, and fill its unique identifier (objref); will > + return 0 if already found in the has, or 1 otherwise [checkpoint] > + > +cr_obj_get_by_ref - return the pointer to the object whose unique identifier > + is equal to objref [restart] > + > +cr_obj_add_ref - add the object with unique identifier objref, pointed to by > + ptr to the hash table if it isn't already there; will return 0 if already > + found in the has, or 1 otherwise [restart]
I'd much rather see all this documentation put properly inline with the source code. I doubt anyone will actually find this stuff.
> + > === Changelog > > [2008-Sep-11] v5: > diff --git a/checkpoint/Makefile b/checkpoint/Makefile > index ac35033..9843fb9 100644 > --- a/checkpoint/Makefile > +++ b/checkpoint/Makefile > @@ -2,5 +2,5 @@ > # Makefile for linux checkpoint/restart. > # > > -obj-$(CONFIG_CHECKPOINT_RESTART) += sys.o checkpoint.o restart.o \ > +obj-$(CONFIG_CHECKPOINT_RESTART) += sys.o checkpoint.o restart.o objhash.o \ > ckpt_mem.o rstr_mem.o > diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c > new file mode 100644 > index 0000000..0862086 > --- /dev/null > +++ b/checkpoint/objhash.c > @@ -0,0 +1,237 @@ > +/* > + * 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/checkpoint.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) > + > +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); > + 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)]; > + hlist_for_each_entry(obj, n, h, hash) > + if (obj->ptr == ptr) > + return obj; > + return NULL; > +} > + > +static struct cr_objref *cr_obj_find_by_objref(struct cr_ctx *ctx, int objref) > +{ > + struct hlist_head *h; > + struct hlist_node *n; > + struct cr_objref *obj; > + > + h = &ctx->objhash->head[hash_ptr((void *) objref, CR_OBJHASH_NBITS)]; > + hlist_for_each_entry(obj, n, h, hash) > + if (obj->objref == objref) > + return obj; > + return NULL; > +} > + > +static struct cr_objref *cr_obj_new(struct cr_ctx *ctx, void *ptr, int objref, > + unsigned short type, unsigned short flags) > +{ > + struct cr_objref *obj; > + > + obj = kmalloc(sizeof(*obj), GFP_KERNEL); > + if (obj) { > + int i; > + > + obj->ptr = ptr; > + obj->type = type; > + obj->flags = flags; > + > + if (objref) { > + /* use 'objref' to index (restart) */ > + obj->objref = objref; > + i = hash_ptr((void *) objref, CR_OBJHASH_NBITS); > + } else { > + /* use 'ptr' to index, assign objref (checkpoint) */ > + obj->objref = ctx->objhash->objref_index++;; > + i = hash_ptr(ptr, CR_OBJHASH_NBITS); > + } > + > + hlist_add_head(&obj->hash, &ctx->objhash->head[i]); > + cr_obj_ref_grab(obj); > + } > + return obj; > +} > + > +/** > + * cr_obj_add_ptr - add an object to the hash table if not already there > + * @ctx: checkpoint context > + * @ptr: pointer to object > + * @objref: unique identifier - object reference [output] > + * @type: object type > + * @flags: object flags > + * > + * Fills the unique identifier of the object into @objref > + * > + * returns 0 if found, 1 if added, < 0 on error > + */ > +int cr_obj_add_ptr(struct cr_ctx *ctx, void *ptr, int *objref, > + unsigned short type, unsigned short flags) > +{ > + struct cr_objref *obj; > + int ret = 0; > + > + obj = cr_obj_find_by_ptr(ctx, ptr); > + if (!obj) { > + obj = cr_obj_new(ctx, ptr, 0, type, flags); > + if (!obj) > + return -ENOMEM; > + else > + ret = 1; > + } else if (obj->type != type) /* sanity check */ > + return -EINVAL; > + *objref = obj->objref; > + return ret; > +} > + > +/** > + * cr_obj_add_ref - add an object with unique identifer to the hash table > + * @ctx: checkpoint context > + * @ptr: pointer to object > + * @objref: unique identifier - object reference > + * @type: object type > + * @flags: object flags > + */ > +int cr_obj_add_ref(struct cr_ctx *ctx, void *ptr, int objref, > + unsigned short type, unsigned short flags) > +{ > + struct cr_objref *obj; > + > + obj = cr_obj_new(ctx, ptr, objref, type, flags); > + return obj ? 0 : -ENOMEM; > +} > + > +/** > + * cr_obj_get_by_ptr - find the unique identifier (objref) of an object > + * @ctx: checkpoint context > + * @ptr: pointer to object > + * @type: object type > + */ > +int cr_obj_get_by_ptr(struct cr_ctx *ctx, void *ptr, unsigned short type) > +{ > + struct cr_objref *obj; > + > + obj = cr_obj_find_by_ptr(ctx, ptr); > + if (obj) > + return obj->type == type ? obj->objref : -EINVAL; > + else > + return -ESRCH; > +} I have some nits about some of that. I'd prefer to see the main code flow of the functions get taken out of the if(){} blocks and put at the first indenting level (cr_obj_new() could use this). One other nit would be to try and get rid of some of the '?:' use. I personally find those hard to read and we don't use them that heavily in the core kernel. For instance, the above can be written:
obj = cr_obj_find_by_ptr(ctx, ptr); if (!obj) return -ESRCH; if (obj->type != type) return -EINVAL; return obj->objref; Which make the error conditions and their results just pop out much easier at the cost of a single added line of code.
-- Dave
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