Print SD card usage in Storage status #124
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The Storage device keeps track of the areas of the SD card that have been accessed during this power cycle. This data can be accessed using the NK_get_SD_usage_data function that returns a range of the SD card that has not been accessed. This data can be used as a guide line when creating new hidden volumes. This patch adds the SD card usage data to the output of the status command for Nitrokey Storage devices.
| let sd_card_usage = device | ||
| .get_sd_card_usage() | ||
| .context("Failed to retrieve SD card usage")?; |
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I am a bit confused by the return value of this function for two reasons:
- I've done nothing else than plugged in the key and the output is:
1% .. 99% not accessed. The documentation states the it should return something<= 100. Any idea why I don't see 100? I tried on two sticks. - I am also confused by the fact that it uses a range with an exclusive upper bound. Are you sure that's correct? I can't seem to read that interpretation from
libnitrokeyitself. It feels as if a user would almost certainly expect a fully inclusive range to be reported at least bynitrocli. What do you think?
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- Well, 99 is <= 100, isn’t it? I get the same output. Unfortunately, there is no documentation for this command. I am glad that I could at least figure out what the usage values mean. So I decided to only guarantee those invariants that I could see in the source code. In this case, there is a unit test that makes sure that 0 <= value <= 100 for both values. I am not sure why the firmware always adds/subtracts one, but I’m inclined to consider it a bug.
- The problem is that there is no documentation, neither in libnitrokey nor in the firmware. If you refer to the
NK_SD_usage_dataandNK_get_SD_usage_datadoc commentsNitrokeyManager.h, I wrote them myself and I tried to keep them as vague as possible as I don’t know the details. I felt like returning aRangeInclusivewould imply a certainty that I did not have. Maybe it would have been better to just return a tuple.
But as we don’t claim to find the largest range and as this is only a guide line for creating a hidden volume, I figured that maybe-off-by-one values are better than no information at all.
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- Well, 99 is <= 100, isn’t it? I get the same output. Unfortunately, there is no documentation for this command. I am glad that I could at least figure out what the usage values mean. So I decided to only guarantee those invariants that I could see in the source code. In this case, there is a unit test that makes sure that 0 <= value <= 100 for both values. I am not sure why the firmware always adds/subtracts one, but I’m inclined to consider it a bug.
Have you talked to the nitrokey guys about that or opened an issue? Seems confusing for users.
- The problem is that there is no documentation, neither in libnitrokey nor in the firmware. If you refer to the
NK_SD_usage_dataandNK_get_SD_usage_datadoc commentsNitrokeyManager.h, I wrote them myself and I tried to keep them as vague as possible as I don’t know the details. I felt like returning aRangeInclusivewould imply a certainty that I did not have. Maybe it would have been better to just return a tuple.But as we don’t claim to find the largest range and as this is only a guide line for creating a hidden volume, I figured that maybe-off-by-one values are better than no information at all.
Sure. I just very much doubt that a half open range would be reported. It just doesn't make any sense to me. In any case, it doesn't matter here.
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Yes, I’m sure I brought it up somewhere, I just can’t remember where. ^^
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Okay, so I played around with it a bit and it appears that it's not so much about accesses but about writes. I read a 1.5 GiB file from my device and nothing changed in the output. It was only after writing to it that I finally saw a change: So I'll change the string to |
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Merged it! Thanks Robin! |
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Thanks! Indeed, while the firmware sends both the read and the write range, |
The Storage device keeps track of the areas of the SD card that have
been accessed during this power cycle. This data can be accessed using
the NK_get_SD_usage_data function that returns a range of the SD card
that has not been accessed. This data can be used as a guide line when
creating new hidden volumes.
This patch adds the SD card usage data to the output of the status
command for Nitrokey Storage devices.