mmc: cache open file descriptors to block devices #4053
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Udev rules can contain a "watch" option, which is described in the man page as: Watch the device node with inotify; when the node is closed after being opened for writing, a change uevent is synthesized. This watch option is enabled by default for all block devices[1]. The intention behind this is to be notified about changes to the partition table. The mmc plugin does however also need to open the block device for writing, even though it never modifies its content, in order to be able to issue ioctls with vendor defined MMC-commands. Reduce the amount of generated change events from one per read to one per collectd runtime by caching the open file descriptor. [1]: https://github.com/systemd/systemd/blob/ef2ad30aee9fa99b0fdb8fe7efda397513cec6af/rules.d/60-block.rules Fixes: 2f15c70 (mmc: add more vendor specific and generic data sources (collectd#4006)) Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>
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mrunge
approved these changes
Sep 28, 2022
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ChangeLog: mmc plugin: cache file descriptors to reduce udev events generated as side-effect
Hi,
there is a slight annoyance when using the eMMC health info support for Micron and Sandisk chips introduced by me in #4006: an udev event is generated on every call to the read callback.
This is due to to the
watchoption that can be used in udev rules, which is described in the man page as:This watch option is enabled by default for all block devices. The intention behind this is to be notified about changes to the partition table. The mmc plugin does however also need to open the block device for writing, even though it never modifies its content, in order to be able to issue
ioctls with vendor defined MMC-commands.Reduce the amount of generated change events from one per read to one per collectd runtime by caching the open file descriptor.
Fixes: 2f15c70 (mmc: add more vendor specific and generic data sources (#4006))
Signed-off-by: Leonard Göhrs l.goehrs@pengutronix.de