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Donenfeld" Subject: Re: [PATCH v1 3/5] treewide: use get_random_u32() when possible Message-ID: References: <20221005214844.2699-1-Jason@zx2c4.com> <20221005214844.2699-4-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-fbdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-wireless@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-sctp@vger.kernel.org, target-devel@vger.kernel.org, linux-mtd@lists.infradead.org, linux-stm32@st-md-mailman.stormreply.com, drbd-dev@lists.linbit.com, dev@openvswitch.org, rds-devel@oss.oracle.com, linux-scsi@vger.kernel.org, dccp@vger.kernel.org, linux-rdma@vger.kernel.org, kasan-dev@googlegroups.com, lvs-devel@vger.kernel.org, Jason Gunthorpe , SHA-cyfmac-dev-list@infineon.com, coreteam@netfilter.org, tipc-discussion@lists.sourceforge.net, linux-ext4@vger.kernel.org, linux-media@vger.kernel.org, linux-actions@lists.infradead.org, linux-nfs@vger.kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-hams@vger.kernel.org, ceph-devel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, cake@lists.bufferbloat.net, brcm80211-dev-list.pdl@broadcom.com, linux-raid@vger. kernel.org, netdev@vger.kernel.org, linux-usb@vger.kernel.org, linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, netfilter-devel@vger.kernel.org, linux-crypto@vger.kernel.org, dmaengine@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Oct 06, 2022 at 07:05:48AM -0600, Jason A. Donenfeld wrote: > On Thu, Oct 6, 2022 at 6:47 AM Jason Gunthorpe wrote: > > On Wed, Oct 05, 2022 at 11:48:42PM +0200, Jason A. Donenfeld wrote: ... > > > - u32 isn = (prandom_u32() & ~7UL) - 1; > > > + u32 isn = (get_random_u32() & ~7UL) - 1; > > > > Maybe this wants to be written as > > > > (prandom_max(U32_MAX >> 7) << 7) | 7 > > ? > > Holy smokes. Yea I guess maybe? It doesn't exactly gain anything or > make the code clearer though, and is a little bit more magical than > I'd like on a first pass. Shouldn't the two first 7s to be 3s? ... > > > - psn = prandom_u32() & 0xffffff; > > > + psn = get_random_u32() & 0xffffff; > > > > prandom_max(0xffffff + 1) > > That'd work, but again it's not more clear. Authors here are going for > a 24-bit number, and masking seems like a clear way to express that. We have some 24-bit APIs (and 48-bit) already in kernel, why not to have get_random_u24() ? -- With Best Regards, Andy Shevchenko