Nish Aravamudan wrote:
On 7/31/05, Raseel Bhagat <rabhagat@xxxxxxxxxx> wrote:
Hi,
I'm very newbie trying to browse the kernel source and especially the
device driver code written in it.
Currently I'm loking at the Uniform Cdrom Driver in
.../linux/drivers/cdrom/cdrom.c
I'm a bit confused about the _SIGNIFICANCE_ AND _USABILITY_ of the macro
:ENSURE .
Did you try reading the comments before said macro?
"/* This macro makes sure we don't have to check on cdrom_device_ops
* existence in the run-time routines below. Change_capability is a
* hack to have the capability flags defined const, while we can still
* change it here without gcc complaining at every line.
*/"
And for reference, here's the #define:
#define ENSURE(call, bits) if (cdo->call == NULL) *change_capability &= ~(bits)
Hi ,
I did read the comment, but I was confused because the
'change_capability' variable is not reassigned to 'cdo->capability'.
What I mean is , once ENSURE is executed, shouldn't the next step be
cdo->capabilty = *change_capability;
And anyways, the CDROM_CAN macro is used for masking the cdo->capability
everywhere else in the code.
1) It's a hack, but it works.
2) Basically, all it does is see if the function is defined for a
particular cdrom_device_ops struct. If it isn't (i.e., the member is
NULL), then we remove those capability bits.
Yeah, I got this part. But to remove the "capability", the
cdo->capability needs to be masked which is done by
CDROM_CAN macro. Hence, I was wondering if there was any other specific
significance of ENSURE macro.
In any case, I just explained the code. What are you actually trying
to find out?
Thanks,
Nish
Are my comprehensions to the above code accurate ?
P.S. Please always state which kernel you are looking at when
referring to any given file -- things in Linux change quite often :)
I'm sorry. It was extremely negligent on my part to not have mentioned
the Kernel.
I am working on the olf 2.4.20 kernel.
--
Thanking You,
Raseel Bhagat
Software Engineer
Nortel-BU BSC-PST (Simulators)
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