Re: [glibc PATCH] fcntl: put F_OFD_* constants under #ifdef __USE_FILE_OFFSET64

[Mike Frysinger <vapier at gentoo dot org>]

On 17 Aug 2016 10:47, Jeff Layton wrote:
> The Linux kernel expects a flock64 structure whenever you use OFD locks
> with fcntl64. Unfortunately, you can currently build a 32-bit program
> that passes in a struct flock when it calls fcntl64.
> 
> Only define the F_OFD_* constants when __USE_FILE_OFFSET64 is also
> defined, so that the build fails in this situation rather than
> producing a broken binary.

this seems to be going against the glibc API/guarantees we've provided
before (or at least tried to promise), and what the fcntl(2) man page
says now.  namely, we haven't documented F_GETLK64 or struct flock64,
with the expectation that the user just calls fcntl() with a struct
flock.  in fact, the man page even goes so far as to discourage people
from using the *64 variants.

it should be possible using our existing LFS framework to make the OFD
cmds available even to 32-bit apps (where sizeof(off_t) == 32).  but
maybe the usage of F_GETLK64/struct flock64/etc... in the real world
has made it hard to put that genie back in the bottle ?  we'd have to
version the current fcntl symbol, create a new fcntl symbol that does
32->64 munging, and add a new fcntl64 symbol that we'd transparently
rewrite to when LFS is turned on.
-mike

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