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Message-Id: <5DA86D3D020000A10003462F@gwsmtp.uni-regensburg.de> Date: Thu, 17 Oct 2019 15:31:41 +0200 From: "Ulrich Windl" <Ulrich.Windl@...uni-regensburg.de> To: <linux-kernel@...r.kernel.org> Subject: Issue with reading sysfs files Hi! I wrote a simple tool to browse sysfs. However I noticed that there are some files having "r" (read) permission, but when you actually try to read from those, I get an I/O error. So I wonder whether the actual read was forgotten to implement, or the read permission should be gone actually. It seems to be implemented correctly in uevent, like # ll /sys/module/drm/uevent --w------- 1 root root 4096 Sep 24 12:24 /sys/module/drm/uevent but it is not (e.g.) for # ll /sys/devices/LNXSYSTM:00/LNXPWRBN:00/input/input1/event1/power/autosuspend_delay_ms -rw-r--r-- 1 root root 4096 Sep 26 14:03 /sys/devices/LNXSYSTM:00/LNXPWRBN:00/input/input1/event1/power/autosuspend_delay_ms # cat /sys/devices/LNXSYSTM:00/LNXPWRBN:00/input/input1/event1/power/autosuspend_delay_ms cat: '/sys/devices/LNXSYSTM:00/LNXPWRBN:00/input/input1/event1/power/autosuspend_delay_ms': Input/output error Here's a summary of such candidates: .../power/autosuspend_delay_ms # ll /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/host2/rport-2:0-0/target2:0:0/2:0:0:1/block/sdb/queue/wbt_lat_usec -rw-r--r-- 1 root root 4096 Sep 26 14:03 /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/host2/rport-2:0-0/target2:0:0/2:0:0:1/block/sdb/queue/wbt_lat_usec # cat /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/host2/rport-2:0-0/target2:0:0/2:0:0:1/block/sdb/queue/wbt_lat_usec cat: '/sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/host2/rport-2:0-0/target2:0:0/2:0:0:1/block/sdb/queue/wbt_lat_usec': Invalid argument # ll /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/resource0 -rw------- 1 root root 4096 Sep 26 14:03 /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/resource0 # cat /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/resource0 cat: '/sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/resource0': Input/output error /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/resource2_wc # ll /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/rom -rw------- 1 root root 262144 Sep 26 14:03 /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/rom # cat /sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/rom cat: '/sys/devices/pci0000:00/0000:00:03.1/0000:01:00.0/rom': Invalid argument # ll /sys/devices/pci0000:80/0000:80:01.1/0000:81:00.0/net/em1/phys_port_id -r--r--r-- 1 root root 4096 Sep 26 14:03 /sys/devices/pci0000:80/0000:80:01.1/0000:81:00.0/net/em1/phys_port_id # cat /sys/devices/pci0000:80/0000:80:01.1/0000:81:00.0/net/em1/phys_port_id cat: '/sys/devices/pci0000:80/0000:80:01.1/0000:81:00.0/net/em1/phys_port_id': Operation not supported .../net/em1/phys_port_name .../net/em1/phys_switch_id # ll /sys/devices/pci0000:80/0000:80:01.2/0000:82:00.0/0000:83:00.0/graphics/fb0/bl_curve -rw-r--r-- 1 root root 4096 Sep 26 14:03 /sys/devices/pci0000:80/0000:80:01.2/0000:82:00.0/0000:83:00.0/graphics/fb0/bl_curve # cat /sys/devices/pci0000:80/0000:80:01.2/0000:82:00.0/0000:83:00.0/graphics/fb0/bl_curve cat: '/sys/devices/pci0000:80/0000:80:01.2/0000:82:00.0/0000:83:00.0/graphics/fb0/bl_curve': No such device # ll /sys/devices/pci0000:80/0000:80:08.1/0000:86:00.2/ata1/host1/scsi_host/host1/em_buffer -rw-r--r-- 1 root root 4096 Oct 17 15:25 /sys/devices/pci0000:80/0000:80:08.1/0000:86:00.2/ata1/host1/scsi_host/host1/em_buffer # cat /sys/devices/pci0000:80/0000:80:08.1/0000:86:00.2/ata1/host1/scsi_host/host1/em_buffer cat: '/sys/devices/pci0000:80/0000:80:08.1/0000:86:00.2/ata1/host1/scsi_host/host1/em_buffer': Invalid argument .../em_message # ll /sys/devices/pci0000:c0/0000:c0:01.1/0000:c1:00.0/host0/scsi_host/host0/fw_crash_buffer -rw-r--r-- 1 root root 4096 Sep 26 14:03 /sys/devices/pci0000:c0/0000:c0:01.1/0000:c1:00.0/host0/scsi_host/host0/fw_crash_buffer # cat /sys/devices/pci0000:c0/0000:c0:01.1/0000:c1:00.0/host0/scsi_host/host0/fw_crash_buffer cat: '/sys/devices/pci0000:c0/0000:c0:01.1/0000:c1:00.0/host0/scsi_host/host0/fw_crash_buffer': Invalid argument # ll /sys/devices/pci0000:c0/0000:c0:01.1/0000:c1:00.0/host0/target0:2:0/0:2:0:0/block/sda/sda1/trace/act_mask -rw-r--r-- 1 root root 4096 Sep 26 14:03 /sys/devices/pci0000:c0/0000:c0:01.1/0000:c1:00.0/host0/target0:2:0/0:2:0:0/block/sda/sda1/trace/act_mask # cat /sys/devices/pci0000:c0/0000:c0:01.1/0000:c1:00.0/host0/target0:2:0/0:2:0:0/block/sda/sda1/trace/act_mask cat: '/sys/devices/pci0000:c0/0000:c0:01.1/0000:c1:00.0/host0/target0:2:0/0:2:0:0/block/sda/sda1/trace/act_mask': No such device or address .../block/sda/sda1/trace/enable .../block/sda/sda1/trace/end_lba .../block/sda/sda1/trace/pid .../block/sda/sda1/trace/start_lba # ll /sys/devices/virtual/net/lo/duplex -r--r--r-- 1 root root 4096 Sep 24 12:30 /sys/devices/virtual/net/lo/duplex # cat /sys/devices/virtual/net/lo/duplex cat: /sys/devices/virtual/net/lo/duplex: Invalid argument # ll /sys/devices/virtual/net/lo/name_assign_type -r--r--r-- 1 root root 4096 Sep 24 12:24 /sys/devices/virtual/net/lo/name_assign_type # cat /sys/devices/virtual/net/lo/name_assign_type cat: /sys/devices/virtual/net/lo/name_assign_type: Invalid argument /sys/devices/virtual/net/lo/speed Found in 4.12.14-95.6-default of SLES SP4 (x86_64) Regards, Ulrich
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