Messages in this thread | | | From | Arnd Bergmann <> | Date | Tue, 14 Nov 2017 13:37:42 +0100 | Subject | Re: [PATCH] debugfs: fix debugfs_real_fops() build error |
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On Tue, Nov 14, 2017 at 12:50 PM, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote: > On Tue, Nov 14, 2017 at 12:40:31PM +0100, Arnd Bergmann wrote: >> Some drivers use debugfs_real_fops() even when CONFIG_DEBUG_FS is disabled, >> which now leads to a build error: >> >> In file included from include/linux/list.h:9:0, >> from include/linux/wait.h:7, >> from include/linux/wait_bit.h:8, >> from include/linux/fs.h:6, >> from drivers/net/wireless/broadcom/b43legacy/debugfs.c:26: >> drivers/net/wireless/broadcom/b43legacy/debugfs.c: In function 'b43legacy_debugfs_read': >> drivers/net/wireless/broadcom/b43legacy/debugfs.c:224:23: error: implicit declaration of function 'debugfs_real_fops'; did you mean 'debugfs_create_bool'? [-Werror=implicit-function-declaration] >> >> My first impulse was to add another 'static inline' dummy function >> returning NULL for it, which would work fine. However, most callers >> feed the pointer into container_of(), so it seems a little dangerous >> here. Since all the callers are inside of a read/write file operation >> that gets eliminated in this configuration, so having an 'extern' >> declaration seems better here. If it ever gets used in a dangerous >> way, that will now result in a link error. > > Ok, but does your patch really "fix" anything? The linker should now > complain, not the compiler, for these types of configurations?
As I said, all calls to debugfs_real_fops() are from a read/write file operation, which gets discarded when CONFIG_DEBUG_FS is disabled, because debugfs_create_file() and similar functions don't use the file_operations structure pointing to them.
There is no link error, unless someone uses debugfs_real_fops() in a function that does not get discarded. If we ever get a function calling debugfs_real_fops() when DEBUG_FS is turned off and we call that function from somewhere else, we definitely want to get the link error over dereferencing container_of(NULL, type, member).
Arnd
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