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I'll be very interested to see if Linus bites at all. This is probably the most sympathetic I've been to the Kernel breaking userspace programs that rely on ba

I'll be very interested to see if Linus bites at all. This is probably the most sympathetic I've been to the Kernel breaking userspace programs that rely on bad behaviour, but Linus has been pretty clear on the matter in the past. > WE DO NOT BREAK USERSPACE! https://lkml.org/lkml/2012/12/23/75 https://lkml.org/lkml/2012/12/23/75

Arnavion 5y ago
Eh, Linux has broken userspace in the past. Twice for me personally in the last ~10 years, one of which could've resulted in hardware damage if the stars had aligned slightly differently :D I wouldn't count it out.
- josephcsible 5y ago
  Are you sure you don't mean it's broken out-of-tree drivers? What exactly did it break?
  - Arnavion 5y ago
    No out-of-tree drivers. 1. https://github.com/torvalds/linux/commit/6b99e3569ba17b9fd38514d66591ae728b778e3b https://github.com/torvalds/linux/commit/6b99e3569ba17b9fd38... (2017) This changed the userspace hwmon API of the thinkpad-acpi driver from `/sys/devices/platform/thinkpad_hwmon/` to `/sys/class/hwmon/hwmon1/`, which broke the sensor-monitoring software that I wrote for my laptop. It was justified on the basis that libsensors was resilient to this change, but my software didn't use libsensors. 2. https://github.com/torvalds/linux/commit/b02c6857389da66b09e447103bdb247ccd182456 https://github.com/torvalds/linux/commit/b02c6857389da66b09e... (2020) This changed the userspace hwmon API of the k10temp hwmon driver, specifically by swapping which temperatures referred to Tctl vs Tdie. For example, my Threadripper reports one real temperature and one fake temperature that's 27degC higher than the real one. (AMD does this because it wants default fan curves to think the CPU is hotter than it really is, because it wants fans to run faster by default.) Since this change swapped the two sensors, it could've had one of two outcomes for fan curve software: - a) Software that monitored the fake temperature was now reading the real temperature, and thus running the fan slower than it needed to. - b) Software that monitored the real temperature was now reading the fake temperature, and thus running the fan faster than it needed to. Luckily my case was (b), so I discovered the change not because of a throttled / smoking CPU but because of an unexpectedly loud CPU fan. (There was another case in ~2012 when the thinkpad-acpi driver switched from procfs to sysfs, but that one was more "justified" because sysfs was the right place for hwmon anyway.)
    - cozzyd 5y ago
      Stuff in /sys/class changes all the time (maybe not so much on normal computers, but on semi-embedded ARM platforms they see to change a lot)

Arnavion 5y ago

Eh, Linux has broken userspace in the past. Twice for me personally in the last ~10 years, one of which could've resulted in hardware damage if the stars had aligned slightly differently :D I wouldn't count it out.

josephcsible 5y ago
Are you sure you don't mean it's broken out-of-tree drivers? What exactly did it break?
- Arnavion 5y ago
  No out-of-tree drivers. 1. https://github.com/torvalds/linux/commit/6b99e3569ba17b9fd38514d66591ae728b778e3b https://github.com/torvalds/linux/commit/6b99e3569ba17b9fd38... (2017) This changed the userspace hwmon API of the thinkpad-acpi driver from `/sys/devices/platform/thinkpad_hwmon/` to `/sys/class/hwmon/hwmon1/`, which broke the sensor-monitoring software that I wrote for my laptop. It was justified on the basis that libsensors was resilient to this change, but my software didn't use libsensors. 2. https://github.com/torvalds/linux/commit/b02c6857389da66b09e447103bdb247ccd182456 https://github.com/torvalds/linux/commit/b02c6857389da66b09e... (2020) This changed the userspace hwmon API of the k10temp hwmon driver, specifically by swapping which temperatures referred to Tctl vs Tdie. For example, my Threadripper reports one real temperature and one fake temperature that's 27degC higher than the real one. (AMD does this because it wants default fan curves to think the CPU is hotter than it really is, because it wants fans to run faster by default.) Since this change swapped the two sensors, it could've had one of two outcomes for fan curve software: - a) Software that monitored the fake temperature was now reading the real temperature, and thus running the fan slower than it needed to. - b) Software that monitored the real temperature was now reading the fake temperature, and thus running the fan faster than it needed to. Luckily my case was (b), so I discovered the change not because of a throttled / smoking CPU but because of an unexpectedly loud CPU fan. (There was another case in ~2012 when the thinkpad-acpi driver switched from procfs to sysfs, but that one was more "justified" because sysfs was the right place for hwmon anyway.)
  - cozzyd 5y ago
    Stuff in /sys/class changes all the time (maybe not so much on normal computers, but on semi-embedded ARM platforms they see to change a lot)