From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Date: Wed, 23 Sep 2020 17:05:27 +0000 Subject: Re: [PATCH 5/9] fs: remove various compat readv/writev helpers Message-Id: <20200923170527.GQ3421308@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: <20200923163831.GO3421308@ZenIV.linux.org.uk> To: Christoph Hellwig Cc: Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , David Laight , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org On Wed, Sep 23, 2020 at 05:38:31PM +0100, Al Viro wrote: > On Wed, Sep 23, 2020 at 03:59:01PM +0100, Al Viro wrote: > > > > That's a very good question. But it does not just compile but actually > > > works. Probably because all the syscall wrappers mean that we don't > > > actually generate the normal names. I just tried this: > > > > > > --- a/include/linux/syscalls.h > > > +++ b/include/linux/syscalls.h > > > @@ -468,7 +468,7 @@ asmlinkage long sys_lseek(unsigned int fd, off_t offset, > > > asmlinkage long sys_read(unsigned int fd, char __user *buf, size_t count); > > > asmlinkage long sys_write(unsigned int fd, const char __user *buf, > > > size_t count); > > > -asmlinkage long sys_readv(unsigned long fd, > > > +asmlinkage long sys_readv(void *fd, > > > > > > for fun, and the compiler doesn't care either.. > > > > Try to build it for sparc or ppc... > > FWIW, declarations in syscalls.h used to serve 4 purposes: > 1) syscall table initializers needed symbols declared > 2) direct calls needed the same > 3) catching mismatches between the declarations and definitions > 4) centralized list of all syscalls > > (2) has been (thankfully) reduced for some time; in any case, ksys_... is > used for the remaining ones. > > (1) and (3) are served by syscalls.h in architectures other than x86, arm64 > and s390. On those 3 (1) is done otherwise (near the syscall table initializer) > and (3) is not done at all. > > 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? Just to make it clear - I do not propose to fold that into this series; there we just need to keep those declarations in sync with fs/read_write.c