Messages in this thread | | | Date | Tue, 20 Sep 2005 15:20:18 +0300 (EEST) | From | Pekka J Enberg <> | Subject | Re: p = kmalloc(sizeof(*p), ) |
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Hi Russell,
On Tue, 20 Sep 2005, Russell King wrote: > Think about it some more. You've added a new member to struct foo. > You want to fix up all the places which allocate struct foo to > initialise this new member. Grepping for 'struct foo' returns 100 > files. Grepping for kmalloc in those 100 files returns 100 files. > > Do you open all 100 in an editor and manually try and locate the five > kmalloc instances of this structure, and end up missing some.
Nope. I grep for assignments to other members of that struct.
On Tue, 20 Sep 2005, Russell King wrote: > Or do you do the sane thing and use kmalloc(sizeof(struct foo), ...) > and grep for "kmalloc[[:space:]]*(sizeof[[:space:]]*(struct foo)" > which returns only the five files and fix those up with knowledge > that you've found all the instances?
There are still statically allocated structs left. So neither heuristic for figuring out initialization points is perfect.
On 9/18/05, Russell King <rmk+lkml@arm.linux.org.uk> wrote: > Such shuffling around should be done in easy to review stages so that > bugs can be found, and not a mega patch. This inherently means that > for a structure name change, you don't end up with a new structure > named the same as an old structure. And if you compile-test the > stages, you find out if you missed the problem.
No disagreement here.
On 9/18/05, Russell King <rmk+lkml@arm.linux.org.uk> wrote: > Your solution is better if the only thing you're concerned about is > "are we allocating enough memory for this fixed size structure". > It completely breaks if you are also concerned about "are we doing > correct initialisation" or "are we allocating enough memory for this > variable sized structure" both of which are far more important > questions. > > *especially* when you consider that kmalloc is redzoned and therefore > will catch the kinds of bugs you're suggesting.
Well, yes, but for initialization, I would prefer something like what Al Viro suggested. To me, initialization is a separate issue from kmalloc. I do get your point but I just don't think sizeof(struct foo) is the answer.
In all completeness, I would personally prefer the following form for allocation and initialization which is readable, easy to get right, and highly greppable:
struct foo *p = kmalloc(sizeof *p, ...);
*p = (struct foo) { .bar = ...; };
Unfortunately it doesn't seem like gcc is doing such a good job with it.
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