This week I helped a colleague solve a strange problem which he had encountered. He was modifying some application level code which had to read and write a device driver I had created to control two LEDs on our device. Previously the application code had only written to the driver but the decision was made to control the two LEDs independently which required reading the old state from the driver prior to updating the LED state. Fortunately I had added the ability to read the LED status since it improved my ability to debug the device driver.
The problem was caused by the need to interleave reads and writes to the device driver which under Linux gets treated as a file. Unbeknownst to my colleague, any read or write to a file stream affects the file pointer which keeps track of the location within the file which will be accessed next. A simple device driver has no need of the file pointer concept but since Linux treats devices as files, the standard library code which enables accesses to devices and files keeps track of the supposed file pointer even if it doesn't need to do so. In a standard file access, I should have been able to do a fseek (file seek) to the current position between the read and write calls to fix this issue. Unfortunately, since my device driver is very bare bones, I suspect there was extra call within the device driver needed to handle fseek calls. I used a brute force fix of closing the device driver and re-opening it within the application code.
Somehow this makes me think of the common wisdom from early in my career which suggested one shouldn't change jobs too often lest one be labeled a "job hopper". It turns out that job hopping has given me a very diverse background which has improved my chances of finding jobs. Changing jobs more frequently has helped me escape from jobs where the work was boring or which placed me under managers which were difficult to deal with.
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