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Goncalves" , "Steve McIntyre" <93sam@debian.org>, joaoanandalima@gmail.com, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-rt-devel@lists.linux.dev Message-Id: In-Reply-To: <20261005232250.2620-1-singhpra@juniper.net> References: <20261005232250.2620-1-singhpra@juniper.net> Subject: Re: [PATCH v5] efivarfs: add nostatfs mount option to skip QueryVariableInfo() Content-Type: text/plain Content-Transfer-Encoding: 7bit Hello Prashant, Thanks for respinning this. On Tue, 6 Oct 2026, at 01:22, Prashant Singh wrote: > QueryVariableInfo() is an EFI runtime service that, on some firmware, > takes tens of milliseconds and runs with preemption disabled, stalling > the CPU that services it (and, on firmware that services it via SMM, all > CPUs). efivarfs_statfs() calls it (rate-limited since commit b2326338dc68 > ("efivarfs: Rate limit statfs() handler")) to report the variable-store > used/available capacity, so any statfs(2) -- e.g. every "df" -- can > inject that stall into unrelated latency-sensitive workloads. > > Add a negatable "nostatfs" mount option: with nostatfs, statfs(2) skips > QueryVariableInfo() and reports zero used/available; with statfs it > reports the capacity as before. It defaults to nostatfs on > CONFIG_PREEMPT_RT so real-time kernels do not take the stall out of the > box, but statfs can be passed there to force reporting back on -- e.g. > for tools such as fwupd that need the efivars free space to update Secure > Boot key databases. > > The option can also be toggled on a live mount via remount, so reporting > can be enabled only for the duration of a firmware update without > unmounting the boot-time efivarfs mount: > > mount -o remount,statfs /sys/firmware/efi/efivars # reporting on > mount -o remount,nostatfs /sys/firmware/efi/efivars # reporting off > > A remount that does not specify statfs/nostatfs keeps the current setting. > So what happens with uid= /gid= in this case. Do they get reset to the default or not? And before this patch?