Empty attribute results into EIO

[jurenat]

When I use iio_info I can see in the log IO errors when accessing the devices' trigger. This is because the current_trigger is empty and reading the file results in reading zero bytes. Is this the desired behavior? When I change this line to accept zero as a valid result, the error disappears but the library thinks that the device does not have a trigger at all.

The iio_info output:

        iio:device2: lis3dh (buffer capable)
                4 channels found:
                        accel_x:  (input, index: 0, format: le:s12/16>>4)
                        3 channel-specific attributes found:
                                attr  0: raw value: -72
                                attr  1: scale value: 0.009806
                                attr  2: scale_available value: 0.009806 0.019613 0.039226 0.117679
                        accel_y:  (input, index: 1, format: le:s12/16>>4)
                        3 channel-specific attributes found:
                                attr  0: raw value: 4
                                attr  1: scale value: 0.009806
                                attr  2: scale_available value: 0.009806 0.019613 0.039226 0.117679
                        accel_z:  (input, index: 2, format: le:s12/16>>4)
                        3 channel-specific attributes found:
                                attr  0: raw value: -980
                                attr  1: scale value: 0.009806
                                attr  2: scale_available value: 0.009806 0.019613 0.039226 0.117679
                        timestamp:  (input, index: 3, format: le:S64/64>>0)
                4 device-specific attributes found:
                                attr  0: current_timestamp_clock value: realtime

                                attr  1: mount_matrix value: 1, 0, 0; 0, 1, 0; 0, 0, 1
                                attr  2: sampling_frequency value: 1
                                attr  3: sampling_frequency_available value: 1 10 25 50 100 200 400 1600
                2 buffer-specific attributes found:
                                attr  0: data_available value: 0
                                attr  1: watermark value: 1
                1 debug attributes found:
                                debug attr  0: direct_reg_access value: 0x0
ERROR: checking for trigger : Input/output error (5)
        iio:device3: 48003000.adc:adc@0 (buffer capable)
                2 channels found:
                        voltage9:  (input, index: 0, format: le:u12/16>>0)
                        3 channel-specific attributes found:
                                attr  0: offset value: 0
                                attr  1: raw value: 1294
                                attr  2: scale value: 0.610351562
                        voltage19:  (input, index: 1, format: le:u12/16>>0)
                        3 channel-specific attributes found:
                                attr  0: offset value: 0
                                attr  1: raw value: 1297
                                attr  2: scale value: 0.610351562
                4 device-specific attributes found:
                                attr  0: oversampling_ratio value: 1
                                attr  1: oversampling_ratio_available value: 1 2 4 8 16 32 64 128 256 512 1024
                                attr  2: trigger_polarity value: rising-edge
                                attr  3: trigger_polarity_available value: rising-edge falling-edge both-edges
                2 buffer-specific attributes found:
                                attr  0: data_available value: 0
                                attr  1: watermark value: 1
                7 debug attributes found:
                                debug attr  0: lincalfact6 value: 512
                                debug attr  1: lincalfact5 value: 537395712
                                debug attr  2: lincalfact4 value: 536347136
                                debug attr  3: lincalfact3 value: 537395712
                                debug attr  4: lincalfact2 value: 536347135
                                debug attr  5: lincalfact1 value: 538443263
                                debug attr  6: direct_reg_access value: 0x100A
ERROR: checking for trigger : Input/output error (5)

[pcercuei]

Can you confirm that #1065 fixes your problem?

(The commit is on top of the main branch which has a lot of API changes, if you are still using v0.25, you can cherry-pick the fix on top of the libiio-v0 branch to test locally)

[darkmoon32]

Yes, this resolves the issue for libiio-v0 branch.

[pcercuei]

Thanks. I'll cherry-pick the commit to libiio-v0 as soon as the PR is merged.