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) 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. This a particularly nasty macro, as it assumes something called cdo exists and something called change_capability exists. But it's only used in the register function and then immediately #undef'd. In any case, I just explained the code. What are you actually trying to find out? Thanks, Nish P.S. Please always state which kernel you are looking at when referring to any given file -- things in Linux change quite often :) -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
