On 06/22/2015 01:26 PM, Markus Armbruster wrote: > This is particularly useful when we abort in error_propagate(), > because there the stack backtrace doesn't lead to where the error was > created. Looks like this: > > Unexpected error at /work/armbru/qemu/blockdev.c:322: > qemu-system-x86_64: -drive if=none,werror=foo: 'foo' invalid write error > action > Aborted (core dumped) > [Exit 134 (SIGABRT)] > > Note: to get this example output, I monkey-patched drive_new() to pass > &error_abort to blockdev_init(). > > To keep the error handling boiler plate from growing even more, all > error_setFOO() become macros expanding into error_setFOO_internal() > with additional __FILE__, __LINE__ arguments. Not exactly pretty, but > it works.
I agree with Laszlo that adding __func__ to the mix also helps. > > The macro trickery breaks down when you take the address of an > error_setFOO(). Fortunately, we do that in just one place: qemu-ga's > Windows VSS provider and requester DLL wants to call > error_setg_win32() through a function pointer "to avoid linking glib > to the DLL". Use error_setg_win32_internal() there. The use of the > function pointer is already wrapped in a macro, so the churn isn't > bad. > > Code size increases by some 14KiB for me (0.3%). Tolerable. Could be > less if we passed relative rather than absolute source file names to > the compiler. I also like it. > +#define error_setg(errp, fmt, ...) \ > + error_setg_internal((errp), __FILE__, __LINE__, (fmt), ## __VA_ARGS__) > +void error_setg_internal(Error **errp, const char *src, int line, > + const char *fmt, ...) GCC_FMT_ATTR(4, 5); > > +#define error_setg_errno(errp, os_error, fmt, ...) \ > + error_setg_errno_internal((errp), __FILE__, __LINE__, (os_error), \ > + (fmt), ## __VA_ARGS__) Nit - why the difference in \ alignment? Nit - as used here, 'errp', 'fmt', and 'os_error' can be used unambiguously; you don't need '(errp)' given the context of a parenthesized comma-separated list (even if someone DID want to unusual by passing in '(a,b)' with a comma operator for their 'errp' argument, they'd have to supply the () because of the semantics of making the macro call). Nit - '## __VA_ARGS__' is a gcc-ism and not portable C99; but I think clang supports it, and we don't really care about other compilers at the moment. At any rate, we already use it elsewhere in qemu.git. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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