From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Date: Wed, 23 Sep 2020 19:47:55 +0000 Subject: Re: [PATCH 5/9] fs: remove various compat readv/writev helpers Message-Id: <20200923194755.GR3421308@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit List-Id: References: <20200923060547.16903-1-hch@lst.de> <20200923060547.16903-6-hch@lst.de> <20200923142549.GK3421308@ZenIV.linux.org.uk> <20200923143251.GA14062@lst.de> <20200923145901.GN3421308@ZenIV.linux.org.uk> <20200923163831.GO3421308@ZenIV.linux.org.uk> In-Reply-To: To: Arnd Bergmann Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , David Howells , David Laight , Linux ARM , "linux-kernel@vger.kernel.org" , "open list:BROADCOM NVRAM DRIVER" , Parisc List , linuxppc-dev , linux-s390 , sparclinux , linux-block , linux-scsi , Linux FS-devel Mailing List , linux-aio , io-uring@vger.kernel.org, linux-arch , Linux-MM , Networking , keyrings@vger.kernel.org, LSM List On Wed, Sep 23, 2020 at 08:45:51PM +0200, Arnd Bergmann wrote: > On Wed, Sep 23, 2020 at 6:38 PM Al Viro wrote: > > > > I wonder if we should do something like > > > > SYSCALL_DECLARE3(readv, unsigned long, fd, const struct iovec __user *, vec, > > unsigned long, vlen); > > in syscalls.h instead, and not under that ifdef. > > > > Let it expand to declaration of sys_...() in generic case and, on x86, into > > __do_sys_...() and __ia32_sys_...()/__x64_sys_...(), with types matching > > what SYSCALL_DEFINE ends up using. > > > > Similar macro would cover compat_sys_...() declarations. That would > > restore mismatch checking for x86 and friends. AFAICS, the cost wouldn't > > be terribly high - cpp would have more to chew through in syscalls.h, > > but it shouldn't be all that costly. Famous last words, of course... > > > > Does anybody see fundamental problems with that? > > I've had some ideas along those lines in the past and I think it should work. > > As a variation of this, the SYSCALL_DEFINEx() macros could go away > entirely, leaving only the macro instantiations from the header to > require that syntax. It would require first changing the remaining > architectures to build the syscall table from C code instead of > assembler though. > > Regardless of that, another advantage of having the SYSCALL_DECLAREx() > would be the ability to include that header file from elsewhere with a different > macro definition to create a machine-readable version of the interface when > combined with the syscall.tbl files. This could be used to create a user > space stub for calling into the low-level syscall regardless of the > libc interfaces, > or for synchronizing the interfaces with strace, qemu-user, or anything that > needs to deal with the low-level interface. FWIW, after playing with that for a while... Do we really want the compat_sys_...() declarations to live in linux/compat.h? Most of the users of that file don't want those; why not move them to linux/syscalls.h? Reason: there's a lot more users of linux/compat.h than those of linux/syscalls.h - it's pulled by everything in the networking stack, for starters...