On Mon, 2006-06-26 at 15:59 +0100, Darryl Miles wrote:
> I do not believe the kernel has any problem with super-large fd_set's
> being passed to it. I believe the kernel will use whatever size its
> given and attempt to access the memory based on the 'maxfd' argument to
> select. If the kernel attempts to access illegal memory from userspace
> context (which the select() syscall runs in) the select() will return
> EFAULT or SIGSEGV the application. So no "recompile the kernel" is needed.
Understood.
OK I implemented the sample source code as provided and it works fine.
Thanks a million! I guess I "must" use this hack. So be it.
Thanks again for all you're help I learned a lot.
I hope the OpenSSL maintainers heard this cry (even if it is a small
cry) and will at some point decide to use a better method than select.
Cheers
Leon
> The "ulimit -a" resources are set per process yes. This affect the
> allocation of new file descriptors within the kernel. The default for
> Fedora and its glibc build is 1024. In order for you to have
> descriptors above 1024 you must have already dealt with raising the
> ulimit. At that point you run into these sorts of problems with any
> auxiliary library your applications call that do IO with select(). So
> you may need to audit other things YMMV.
>
> Its purely a userspace issue.
>
> Maybe in rand/rand_unix.c you can replace 'fd_set' with 'my_fd_set',
> then at the top of the code put:
>
> #include <sys/select.h>
> #define I_WANT_FD_SETSIZE 2048
>
> #ifndef _NFDBITS
> #define _NFDBITS 8
> #endif
> #ifdef __fd_mask
> /* probably not perfect for x86_64 */
> #define __fd_mask long int __fd_mask
> #endif
>
> struct my_fd_set_type {
> __fd_mask fds_bits[I_WANT_FD_SETSIZE / __NFDBITS];
> };
>
> typedef struct my_fd_set_type my_fd_set;
>
>
>
> You need to replace:
>
> fd_set fset;
>
> with
>
> my_fd_set fset;
>
>
>
> You need to replace FD_ZERO(&fset) with:
>
> memset(&my_fd_set, 0, sizeof(my_fd_set));
>
>
> Since the default macro will only clear the bits covering the first 1024
> fds.
>
>
>
> The try as Marek suggests:
>
> FD_SET(fd, (fd_set *)&my_fd_set;
>
> And with select use:
> select(aaa, (fd_set *)&my_fd_set, xxx, yyy, zzz);
>
>
> It is only the userspace code that allocats storage for fd_set type and
> calls FD_ZERO() and FD_SET() that needs to be altered. From there you
> can pass around the address of 'my_fd_set' and ultimately use it on the
> select() call.
>
> If the stock glibc FD_SET() do not work, you may need to implemnt your
> own version of them against your my_fd_set_type. But I dont think this
> is the case I think FD_SET() will work but FD_ZERO() wont. Just use
> memset() for FD_ZERO().
>
>
> The above is pretty Linux / glibc specific. You dont need to recompile
> anything but the single file rand/rand_unix.c from OpenSSL. It is the
> only affected part within OpenSSL AFAIK.
>
> Obviously you may need to audit your application code for the same
> requirements.
>
>
> HTH
>
> Darryl
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