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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-490bc3cc140sm105657875e9.9.2026.06.04.10.38.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Jun 2026 10:38:30 -0700 (PDT) Date: Thu, 4 Jun 2026 18:38:29 +0100 From: David Laight To: Linus Torvalds Cc: Askar Safin , metze@samba.org, akpm@linux-foundation.org, axboe@kernel.dk, brauner@kernel.org, david@kernel.org, dhowells@redhat.com, hch@infradead.org, jack@suse.cz, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, miklos@szeredi.hu, netdev@vger.kernel.org, patches@lists.linux.dev, pfalcato@suse.de, viro@zeniv.linux.org.uk, willy@infradead.org Subject: Re: [PATCH 2/3] vmsplice: make vmsplice a trivial wrapper for preadv2/pwritev2 Message-ID: <20260604183829.63c35fd9@pumpkin> In-Reply-To: References: <20260603211736.755139-1-safinaskar@gmail.com> <20260604100609.6b37f500@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: AD81F1A0005 X-Stat-Signature: y8gtonh7k8n4oj9fweuur5wmjhopfohn X-HE-Tag: 1780594712-801732 X-HE-Meta: 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 XIdDepst 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 4 Jun 2026 07:17:10 -0700 Linus Torvalds wrote: > On Thu, 4 Jun 2026 at 02:06, David Laight wrote: > > > > Something needs to ensure that the high 32bits of the fd get masked off > > on 64bit systems. > > That something already exists: CLASS(fd, f)(fd); > > It ignores the top bits, because 'fdget()' takes an 'unsigned int'. > > We have been a bit random in how we declare the system calls in > general, and we mix 'unsigned int' and 'int' and 'unsigned long' > pretty much randomly when it comes to file descriptor arguments to > system calls. > > fs/read_write.c in particular uses all three cases with no real logic to it all: > > SYSCALL_DEFINE3(lseek, unsigned int, fd, .. > SYSCALL_DEFINE3(readv, unsigned long, fd, .. > SYSCALL_DEFINE4(sendfile, int, out_fd, .. > > but then anything that uses fdget() (through one of the helper classes > or not) will simply not care. > > Does it make sense? Is it pretty? Nope. Does it matter? Also nope. I know it has mattered elsewhere, and is easy to get wrong because 'mostly it works'. At least u32/u64 is reasonably sane - the called function has to ignore the high bits (at least on x86). Bool is another matter entirely, (IIRC from a couple of weeks ago) gcc will assume that the low 8 bits of the parameter register are either 0 or 1 and clang assumes that the low 32 bits are 0 or 1. You can't even check with 'if ((u32)bool_param > 1) error()' because the compiler 'knows' it can't be false. It all dumps you down one of the UB 'rabbit holes'. -- David > > Linus