Messages in this thread | | | Date | Tue, 19 Oct 1999 11:41:22 +0100 (BST) | From | Tigran Aivazian <> | Subject | Re: access_ok inside kernelspace |
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Dear Ingo,
I agree that it should be (and is now) possible to use system calls from within system calls (i.e. by going through int 0x80 via _syscallX(). However, some of the examples you give have nothing to do with this issue.
On Tue, 19 Oct 1999, Ingo Molnar wrote: > some users of this feature: exec() is using fop->read() that is not going through _syscallX(), that is just using a function pointer visible indirectly.
> sys_ustat() is internally using ->statfs() same as above.
> autofs is using ->write(). kNFSd is using > ->read(), ->write(), ->readlink(), ->statfs(). NBD, loopback, etc. same as above.
> this is a regular kernel feature, it gives us flexibility to reuse already > existing functionality internally. yes, reusing the methods that filesystems (or others) provide is a good thing. Going through int 0x80 is *also* a good thing. But they are two completely different things.
> there are even 'deeper' calls than calls to sys_*(), eg. khttpd is using > the socket layer quite directly, to do ->recvmsg(), ->sendmsg(), ->read() > without any demultiplexing overhead and it's using internal socket-layer > data structures directly. [it uses other system calls as well, but only > those need set_fs()/get_fs() which are interacting with user-space VM]
Yes, but you have not shown a single case of calling system calls from within system calls (or from withing any other part of the kernel) via sys_XXX functions. I presume there are none (on i386 architecture)?
All I said is that if the kernel wants to call a system call then it should go through _syscallX() macros. All known to me examples do just that. (but on alpha they do call sys_XXX() functions which is a bit inconsistent but I am sure there is a reason for that).
Of course the examples you gave are valid usages of kernel functions via indirect pointers but NOT of using the system calls.
Regards, ------ Tigran A. Aivazian | http://www.sco.com Escalations Research Group | tel: +44-(0)1923-813796 Santa Cruz Operation Ltd | http://www.ocston.org/~tigran
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