Documentation bugs for scrub limits

[Graham Cobb <g.btrfs@cobb.uk.net>]

I have been playing with the btrfs scrub limits capability and have 
found a few minor problems with the documentation. I am happy to create 
patches for these if that is preferred, but I seem to remember that 
there is a "collected typos and minor documentation fixes" patchset 
occasionally and these might be good candidates for the next one.


1) I (incorrectly) entered: btrfs scrub limit /mnt/snapshots/ -l 100m

The error message was:

       ERROR: --limit must be used with either --all or --deivd

This should be "--devid"


2) The btrfs-scrub manpage shows how to set the limits "using 
/sys/fs/btrfs/FSID/devinfo/DEVID/scrub_speed_max". However, the text 
below explains that the limit can now be set with the --limit option. I 
suggest rewriting this to remove the reference to the scrub_speed_max 
file altogether and adding an example like "btrfs scrub limit --devid 1 
--limit 100m /".


3) It might be useful to give users some help understanding typical 
scrub limits. While there are many possible differences, less 
experienced users would probably not be familiar with what are typical 
useful values (is "100m" a lot?).


4) Related to the point above... The man page explains the "limit" 
option talking about "sizes" and accepts things like "--tbytes". 
Presumably these are really "rates" ("sizes per second")  And it might 
be helpful to mention that things like "--tbytes" are unlikely to ever 
be useful for rates!!


5) Mention that "--si" applies only to display, not to "--limit" values.


6) Mention that the --limit suffices are not case sensitive.


In addition to these documentation issues, I wonder if a small 
functional change might also be useful... The display format for the 
rate limit shows things like "1.07TiB". However, the syntax for setting 
the limit does not allow typing in 1.07TiB (or, even, 1TiB - only 
"1100g" or "1100G").


Graham