lkml.org 
[lkml]   [2008]   [Dec]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC v10][PATCH 09/13] Restore open file descriprtors
From
Date
On Mon, 2008-12-01 at 13:07 -0800, Dave Hansen wrote:
> > When a shared object is inserted to the hash we automatically take another
> > reference to it (according to its type) for as long as it remains in the
> > hash. See: 'cr_obj_ref_grab()' and 'cr_obj_ref_drop()'. So by moving that
> > call higher up, we protect the struct file.
>
> That's kinda (and by kinda I mean really) disgusting. Hiding that two
> levels deep in what is effectively the hash table code where no one will
> ever see it is really bad. It also makes you lazy thinking that the
> hash code will just know how to take references on whatever you give to
> it.
>
> I think cr_obj_ref_grab() is hideous obfuscation and needs to die.
> Let's just do the get_file() directly, please.

Well, I at least see why you need it now. The objhash thing is trying
to be a pretty generic hash implementation and it does need to free the
references up when it is destroyed. Instead of keeping a "hash of
files" and a "hash of pipes" or other shared objects, there's just a
single hash for everything.

One alternative here would be to have an ops-style release function that
gets called instead of what we have now:

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();
}
}
That would make it something like:

struct cr_obj_ops {
int type;
void (*release)(struct cr_objref *obj);
};
void cr_release_file(struct cr_objref *obj)
{
struct file *file = obj->ptr;
put_file(file);
}
struct cr_obj_ops cr_file_ops = {
.type = CR_OBJ_FILE,
.release = cr_release_file,
};

And the add operation becomes:

get_file(file);
new = cr_obj_add_ptr(ctx, file, &objref, &cr_file_ops, 0);

with 'cr_file_ops' basically replacing the CR_OBJ_FILE that got passed
before.

I like that because it only obfuscates what truly needs to be abstracted
out: the release side. Hiding that get_file() is really tricky.

But, I guess we could also just kill cr_obj_ref_grab(), do the
get_file() explicitly and still keep cr_obj_ref_drop() as it is now.

-- Dave



\
 
 \ /
  Last update: 2008-12-02 02:35    [from the cache]
©2003-2011 Jasper Spaans