>> Ucred routines will shrink the actual size of the ucred exchanges: the >> ucred structures will "shrink to fit" and only processes which use a lot >> of groups will pay for this in ucred exchanges. > >How does this work? The size of a ucred is not passed around, but >required to be ucred_size(3C). I guess receiving code will malloc() >ucred_size() bytes, receive the ucred, and realloc() to the correct, >smaller size, which would be encoded in a ucred header. Or perhaps >you'll be enhancing the ucredsys/doorsys syscalls so that you only alloc >as much as needed? Yes, implementation details, I know. But >interesting details nonetheless.
Ucred is currently formatted like this: <header><pcred_t><NGROUPS_MAX * gid_t><privs>[<audit>][<txlabel>] The new generated format is: <header><pcred_t><cr->cr_ngroups * gid_t><privs>[<audit>][<txlabel>] Well, you can't know how big the item you are going to receive and you want to be able to re-use the buffer. (With 1024 groups, you'll need to allocate at least 4K)So in userland you allocate ucred_size(). In the kernel we generate the ucred and we know how big the item is going to be; we allocate as much as we need and we copyout just that data. Casper
