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Fri, 27 Jan 2023 10:46:57 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.9.0-alpha0-85-gd6d859e0cf-fm-20230116.001-gd6d859e0 Mime-Version: 1.0 Message-Id: <54c8ecbd-1d6e-40f1-af30-7efd04c63a7e@app.fastmail.com> In-Reply-To: <20230126175356.1582123-3-nphamcs@gmail.com> References: <20230126175356.1582123-1-nphamcs@gmail.com> <20230126175356.1582123-3-nphamcs@gmail.com> Date: Fri, 27 Jan 2023 16:46:38 +0100 From: "Arnd Bergmann" To: "Nhat Pham" , "Andrew Morton" Cc: "Johannes Weiner" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, bfoster@redhat.com, "Matthew Wilcox" , linux-api@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v8 2/3] cachestat: implement cachestat syscall Content-Type: text/plain X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0F1DD40006 X-Stat-Signature: 1urkhpapyz9aizm4te5431i8nnim7n7x X-HE-Tag: 1674834418-623517 X-HE-Meta: U2FsdGVkX19lbHK5btMt4cfyZY8vU8Auq3WUAxBdbtkXGhfqWYoLrjGEP6Wud1BovBbvELNqvgBg1h6/WNi6ifu7r6jtFq2SdH8gdPRUOx6mKsuryu7hTTF4qg2BWBwWydx6sCftm4A5dhi3tpahX4hhLSKzuCHfAXO1+7Wb14iOSQZMcrrSLaNXaeLOWNDASBDb35BvLzQxFMTJxa3w7ipDnJ9xEvjxj+jKRtxDzX3PMiTQkAz91sWtKx4bPikEy0F0AZVncR7Rt2ZXnkfg4/xFx91UoWCHPYIS+s+eou4Y4lyAh+4B+ARrqHkidNbxas4duCo3M1BDbmKV2mdhEwY8iHmlBtNanuedt+MTrVg3FVdgqviRSaSfxE9s6ehISVxq7QvGfzVx9SYPjUjIHbyPGk/NO4+cA8ygpM2AYThRzL8++lB6/AeyPGi1PEQZU34lK+O6dstBmPiorjxb+ZBNZIx5Xfp7xGKsgpTpHca2Ai1yOwWTlBDIn5wyN6KrHmstlwf4eGQQATbAzfQe0+OOGkHJ2EA6asBLJ3YJ2UdSAxHGNNfeq2WxqqsUyRK2ZgnHpyikcAxFuImvELD6Xa0OV3+2uUPHkcYcJodnwn2ePgL0Qi0/lQA600a1kAAGVJNXXzpEiO9euJUMYFlNwfF75yEgkCK7X+WnarATP7lVhk75aEoIROjNL0cDCwtz6b271d8pz93J0aV1eGSt0BMpzVljNVWZf4j56P9Yj9sYCo7OIB4s0OsufKoe6kiVM5vX9MuIG2W78BdC/nWtnXIKTrgHhJocH8o3Fp4Dm4oo7q0NCIFx53O97HP13noXqThKQIx+87hUL+/jTfB0TxKSkpKKzMsGpNrhyXeCxehMcWb9mewBXdbc6GDETwSugSaJr8OxDoEItxdHp5sKY0PujJ0+BQKZCaxHlKNn4BSaT4ySHC2YAA46o4h2hUmH9B1nkBn4kx55koKUnoB qIcqHt4M D5Z7TJNpBd6esN+PLVy3ptMj24rJa9fD4W2lY2sdqZ4q3QFK+AhJHt8OITa+cp7QGRC+8cRR48wxwcfhhL07uyIjBeMGwkSxFTWQ/VwFlnJVYBuP9KiwB1Y0cfvdXssLYZMTjJVigKnehZjN8J+0anIfpXQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jan 26, 2023, at 18:53, Nhat Pham wrote: > > SYNOPSIS > #include > > struct cachestat { > __u64 nr_cache; > __u64 nr_dirty; > __u64 nr_writeback; > __u64 nr_evicted; > __u64 nr_recently_evicted; > }; > > int cachestat(unsigned int fd, off_t off, size_t len, > unsigned int cstat_version, struct cachestat *cstat, > unsigned int flags); Is this "off_t off" argument intentionally limited to the old 32-bit type on 32-bit architectures? Unfortunately I fear there are no good options to pass an offset here: - if you make it a 32-bit type, this breaks calling it from normal userspace that defines off_t as a 64-bit type - if you change it to a 64-bit loff_t, there are three separate calling conventions for 64-bit, 32-bit with aligned register pairs and other 32-bit, plus you exceed the usual limit of six system call arguments A separate problem may be the cstat_version argument, usually we don't use interface versions but instead use a new system call number if something changes in an incompatible way. Arnd