Messages in this thread | | | Subject | Re: [PATCH][next] UAPI: nfsfh.h: Replace one-element array with flexible-array member | From | "Gustavo A. R. Silva" <> | Date | Fri, 26 Mar 2021 09:10:15 -0500 |
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On 3/26/21 03:17, David Laight wrote: > From: Gustavo A. R. Silva >> Sent: 25 March 2021 21:12 >> >> On 3/25/21 10:29, David Laight wrote: >> >>>>> >>>>> Could you use the simpler: >>>>>> struct nfs_fhbase_new { >>>>>> __u8 fb_version; >>>>>> __u8 fb_auth_type; >>>>>> __u8 fb_fsid_type; >>>>>> __u8 fb_fileid_type; >>>>>> union { >>>>>> __u32 fb_auth[1]; >>>>>> __u32 fb_auth_flex[0]; >>>>>> }; >>>>>> }; >>>>> >>>>> Although I'm not certain flexible arrays are supported >>>>> as the last element of a union. >>>> >>>> Nope; this is not allowed: https://godbolt.org/z/14vd4o8na >>> >>> Nothing an extra 'struct {__u32 fb_auth_flex[0]; }'; won't solve. >> >> We don't want to introduce zero-length arrays [1]. > > I probably meant to write [] not [0] - doesn't affect the idea. > > The real problem is that the compiler is likely to start rejecting > references to a flex array that go beyond the end of the outer > structure. > > Thinking back, isn't fb_auth[] at least one entry long? > So it could be: > > struct nfs_fhbase_new { > __u8 fb_version; > __u8 fb_auth_type; > __u8 fb_fsid_type; > __u8 fb_fileid_type; > __u32 fb_auth[1]; > __u32 fb_auth_extra[]; > };
I don't think this is a great idea because, contrary to the change I'm proposing, in this case memory regions for fb_auth and fb_auth_extra don't actually overlap.
-- Gustavo
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