I'm confused by errno and error handling in gnulib, and what the strategy for this is supposed to be, versus how it seems to work now.
Win32 has two methods to return an error code from a syscall: DWORD WSAGetLastError(void); // for all socket functions DWORD GetLastError(); // for all other system calls Win32 itself doesn't use or define a variable called 'errno', but gnulib does provide this variable when linked to Win32 programs. Unfortunately gnulib also sets errno, in a lot of places. Oh yeah, also error codes aren't compatible with each other -- I'll come to that later. This leads to some quite schizophrenic error handling in my code. I basically have four cases I have to consider: (a) A call to a Winsock socket function that gnulib has replaced: Gnulib calls set_winsock_errno to map the WSAGetLastError into an errno value. So I can check errno or (with the latest version of gnulib) WSAGetLastError. (b) A call to a Winsock socket function that gnulib hasn't replaced: errno won't have any meaningful value and I must call WSAGetLastError. (c) A call to a non-socket Win32 function that gnulib has replaced: I have to go and check Gnulib to see if it sets errno (some do, some don't, some do only along some paths). I need to then consider errno and/or GetLastError. I have to keep checking this with every revision of Gnulib because it might change. (d) A call to a non-socket Win32 function that gnulib hasn't replaced: I only need to check GetLastError. In addition, it turns out that error codes aren't compatible. Although Gnulib tries to define its own error numbers which are compatible with Win32 ones (eg. EINPROGRESS == 10036 == WSAEINPROGRESS), it also uses some from the MinGW header files which are just plain wrong (eg. ENOMEM == 12 == ERROR_INVALID_ACCESS, MinGW gets this wrong, it should be ENOMEM 14 == ERROR_OUTOFMEMORY). So code as in the replacement malloc which sets errno = ENOMEM is not just hard to use because of the factors above, it's also setting errno to an incorrect value. Of course I also want my code to primarily work on Unix too. Before I launch into what I think Gnulib should be doing, first of all is there some strategy for errno / error handling which I'm missing? Has this been discussed before? Am I using errno / error handling incorrectly? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://et.redhat.com/~rjones/virt-df/
