Re: Socket programming question
On Nov 14, 2007 4:55 PM, Heiko Wundram (Beenic) <[EMAIL PROTECTED]> wrote: > > Sorry to say that, but it doesn't make sense as it's worded. The > descriptor > returned by socket(2) is valid if it's >= 0 (that's the API contract for > the > socket(2) C function), and remains valid until the program ends (unless > you > close the descriptor with close(2) before your program terminates, in > which > case the descriptor first becomes invalid [i.e. EBADF], but might be > reused > later by another call to socket(2) or open(2), in which case the > descriptor > again becomes valid but is associated with another object and possibly > also > with another type of object [file/pipe vs. socket]). > > That's the API-contract that's specified in POSIX, and to which FreeBSD > sticks. As an application programmer, you can (and have to) rely on this > behaviour; any derivation from this is a kernel bug, and should be posted > as > a PR. > > Generally, the easy way to query whether a descriptor is valid is by > simply > calling the respective function you want to execute on it, and if that > returns errno = EBADF, then you know that the descriptor is invalid. In > case > it returns something else, it just tells you that the descriptor is valid, > but doesn't tell you whether the descriptor is really associated with what > you think it is. But if you follow the flow of control in the program, you > should be able to make out where the descriptor is created and how it's > modified, and thus be able to deduce (under the condition that the kernel > sticks to POSIX specifications) what the state of the descriptor is at the > time of usage. > Thanks. Actually, this suggestion of yours I think does answer my question. I was thinking that in my testing program, I would be using something like that after thinking things through. Thanks again. Andy ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Socket programming question
On 2007-11-14 15:21, Andrew Falanga <[EMAIL PROTECTED]> wrote: > Hi, > My question has to do with how someone would find out if a call to > socket(2) actually produced a socket. I know that the API works, I've > programmed with it many times, but is there a way to find out if 's' > returned by socket(2) is actually valid in whatever kernel structure > it is stored? I understand that I may have the process entirely mixed > up. But it seems to me that the socket is somehow known to the kernel > and I should be able to query the kernel somehow and discover if it is > valid. The socket() system call returns -1 when it fails. Isn't that sufficient? If not, why? What ``extra'' information would you expect from the kernel when socket() fails? > Let me know if my question doesn't make sense as worded and I'll try > to explain myself better. Another question related to this one, would > someone in this list know where the source code is, in the system > source tree, for the select call? Look for kern_select() in `/usr/src/sys/kern/sys_generic.c'. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Socket programming question
Derek Ragona wrote: With internet sockets, these get added to the TCP stack, and their are kernel structures created too I'm sure, but I have no idea how to find those. Netstat will show sockets in use though. sockstat(1) might also be useful as it shows information about what program opened the connection and the file descriptor number of the socket. -- Bruce ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Socket programming question
Am Mittwoch, 14. November 2007 23:21:43 schrieb Andrew Falanga: > My question has to do with how someone would find out if a call to > socket(2) actually produced a socket. I know that the API works, I've > programmed with it many times, but is there a way to find out if 's' > returned by socket(2) is actually valid in whatever kernel structure it is > stored? I understand that I may have the process entirely mixed up. But > it seems to me that the socket is somehow known to the kernel and I should > be able to query the kernel somehow and discover if it is valid. > > Let me know if my question doesn't make sense as worded and I'll try to > explain myself better. Another question related to this one, would someone > in this list know where the source code is, in the system source tree, for > the select call? Sorry to say that, but it doesn't make sense as it's worded. The descriptor returned by socket(2) is valid if it's >= 0 (that's the API contract for the socket(2) C function), and remains valid until the program ends (unless you close the descriptor with close(2) before your program terminates, in which case the descriptor first becomes invalid [i.e. EBADF], but might be reused later by another call to socket(2) or open(2), in which case the descriptor again becomes valid but is associated with another object and possibly also with another type of object [file/pipe vs. socket]). That's the API-contract that's specified in POSIX, and to which FreeBSD sticks. As an application programmer, you can (and have to) rely on this behaviour; any derivation from this is a kernel bug, and should be posted as a PR. Generally, the easy way to query whether a descriptor is valid is by simply calling the respective function you want to execute on it, and if that returns errno = EBADF, then you know that the descriptor is invalid. In case it returns something else, it just tells you that the descriptor is valid, but doesn't tell you whether the descriptor is really associated with what you think it is. But if you follow the flow of control in the program, you should be able to make out where the descriptor is created and how it's modified, and thus be able to deduce (under the condition that the kernel sticks to POSIX specifications) what the state of the descriptor is at the time of usage. Hope this helps! -- Heiko Wundram Product & Application Development ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: Socket programming question
At 04:21 PM 11/14/2007, Andrew Falanga wrote: Hi, My question has to do with how someone would find out if a call to socket(2) actually produced a socket. I know that the API works, I've programmed with it many times, but is there a way to find out if 's' returned by socket(2) is actually valid in whatever kernel structure it is stored? I understand that I may have the process entirely mixed up. But it seems to me that the socket is somehow known to the kernel and I should be able to query the kernel somehow and discover if it is valid. Let me know if my question doesn't make sense as worded and I'll try to explain myself better. Another question related to this one, would someone in this list know where the source code is, in the system source tree, for the select call? Thanks, Andy Andy, It's been a while since I did socket programing, but the easiest test is to use a client application to contact the server side socket. Just be sure if you want to connect from another host you set the domain correctly in your socket call for a local socket on the same host or an internet socket to contact from another host. With internet sockets, these get added to the TCP stack, and their are kernel structures created too I'm sure, but I have no idea how to find those. Netstat will show sockets in use though. -Derek -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. MailScanner thanks transtec Computers for their support. ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Socket programming question
Hi, My question has to do with how someone would find out if a call to socket(2) actually produced a socket. I know that the API works, I've programmed with it many times, but is there a way to find out if 's' returned by socket(2) is actually valid in whatever kernel structure it is stored? I understand that I may have the process entirely mixed up. But it seems to me that the socket is somehow known to the kernel and I should be able to query the kernel somehow and discover if it is valid. Let me know if my question doesn't make sense as worded and I'll try to explain myself better. Another question related to this one, would someone in this list know where the source code is, in the system source tree, for the select call? Thanks, Andy ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
