[haiku-gsoc] Re: Implementation Queries
- From: Adrien Destugues <pulkomandy@xxxxxxxxxxxxx>
- To: haiku-gsoc@xxxxxxxxxxxxx
- Date: Wed, 28 Jun 2017 07:35:21 +0200
On Wed, Jun 28, 2017 at 05:30:58AM +0530, Vivek Roy wrote:
Okay, on further searching I came across pcmcia/k_compat.h
<http://xref.plausible.coop/source/xref/haiku/headers/os/drivers/pcmcia/k_compat.h>
It reads:
/* Memory allocation. BeOS doesn't have an atomic malloc. */
#define kmalloc(s,f) malloc(s)
#define kfree(p) free(p)
#define kfree_s(p,s) free(p)
void *malloc();
void free(void *);
So I should ignore all flags and just do a malloc(sizeof(kobj)) ?
It depends which flags are used. You didn't tell us which flags kmalloc
is using in your use cases.
If you don't know which flags are used, I would start with something like this:
void* kmalloc(size_t size, uint32_t flags)
{
if (flags & CONTIGUOUS_MEMORY)
PANIC("kmalloc doesn't know how to do contiguous memory yet!");
if (flags & ...)
...
// ok, nothing special required. few!
return malloc(size);
}
On Wed, Jun 28, 2017 at 4:42 AM, Vivek Roy <vivekroyandroid@xxxxxxxxx>
wrote:
Okay, so I was trying to allocate physically non-contiguous memory. I was
looking at Kernel Kit's create_area() to be used in place of kzalloc.
A few things I noted (please let me know if I am wrong):
1. A call to kzalloc expects the memory to be zero-ed out. create_area
doesn't have any such flag so it has to be done by making a call to memset
(We can use memset on the memory returned from create_area right?)
You can use memset, or calloc.
2. I am using the B_ANY_KERNEL_ADDRESS constant for addr_spec parameter of
create_area
Yes, if there are no other constraints on the address, this is fine.
3. The size alllocated has to be a multiple of B_PAGE_SIZE. So for
allocating sizeof(kobj) bytes, I will have to allocate [(sizeof(kobj) +
B_PAGE_SIZE
- 1) / B_PAGE_SIZE] bytes of memory.
I think create_area would take care of this already? Anyway, if
something request a kmalloc of 3 bytes, certainly it shouldn't use a
full B_PAGE_SIZE and just use 3 bytes.
4. For locking constant I think B_LAZY_LOCK should be okay
5. Protection is B_READ_AREA | B_WRITE_AREA
In general, create_area is dedicated to allocating pages of memory. It
is a rather low level operation. This is not always needed, if kmalloc
is used just to allocate some general purmose memory, then a simple
malloc in Haiku would probably do. And creating a dedicated area (of at
least 4 kilobytes) for each allocation, no matter how small, would waste
quite a lot of memory in the end.
I expect you can find if create_area is needed depending on the kmalloc
flags. But, you didn't list which flags are used in your case, so I
don't know which function is best used.
--
Adrien.
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