General TC > Programming & Scripting - Unofficial

Tinkering with rebuildfstab

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Rich:
Hi curaga

--- Quote from: curaga on February 25, 2023, 11:09:43 AM --- ... Everyone is welcome to go over the TC scripts. rebuildfstab's speed is fast enough for me personally, but if you find it too slow, please do look into it. ...
--- End quote ---
I think I may have an approach that doesn't need the  find  command.
The  /dev/block/*  directory seems to contain the information being searched for.
I used a cut down version of  rebuildfstab  containing the  find  loop that isolates
the value of  DEVNAME  and  DEVMAJOR as a baseline. I included an  echo
statement to list the found devices.
Here are the timing results:

--- Code: ---tc@E310:~/rebuildfstab$ time ./findblockdevs > /dev/null
real    0m 0.71s
user    0m 0.22s
sys     0m 0.53s
tc@E310:~/rebuildfstab$ time ./newfindblockdevs  > /dev/null
real    0m 0.09s
user    0m 0.04s
sys     0m 0.05s
tc@E310:~/rebuildfstab$
--- End code ---

It finds the same devices (order does not matter):

--- Code: ---tc@E310:~/rebuildfstab$ time ./findblockdevs
DEVNAME=sda4    DEVMAJOR=8
DEVNAME=sda2    DEVMAJOR=8
DEVNAME=sda     DEVMAJOR=8
DEVNAME=sda7    DEVMAJOR=8
DEVNAME=sda5    DEVMAJOR=8
DEVNAME=sda3    DEVMAJOR=8
DEVNAME=sda1    DEVMAJOR=8
DEVNAME=sda6    DEVMAJOR=8
DEVNAME=sdb     DEVMAJOR=8
DEVNAME=sdb1    DEVMAJOR=8
DEVNAME=sdc     DEVMAJOR=8
DEVNAME=sdd     DEVMAJOR=8
DEVNAME=sde     DEVMAJOR=8
DEVNAME=sdf     DEVMAJOR=8
DEVNAME=sr0     DEVMAJOR=11
DEVNAME=sr1     DEVMAJOR=11
real    0m 0.70s
user    0m 0.22s
sys     0m 0.52s
tc@E310:~/rebuildfstab$ time ./newfindblockdevs
DEVNAME=sr0     DEVMAJOR=11
DEVNAME=sr1     DEVMAJOR=11
DEVNAME=sda     DEVMAJOR=8
DEVNAME=sda1    DEVMAJOR=8
DEVNAME=sdb     DEVMAJOR=8
DEVNAME=sdb1    DEVMAJOR=8
DEVNAME=sda2    DEVMAJOR=8
DEVNAME=sda3    DEVMAJOR=8
DEVNAME=sdc     DEVMAJOR=8
DEVNAME=sda4    DEVMAJOR=8
DEVNAME=sdd     DEVMAJOR=8
DEVNAME=sda5    DEVMAJOR=8
DEVNAME=sda6    DEVMAJOR=8
DEVNAME=sde     DEVMAJOR=8
DEVNAME=sda7    DEVMAJOR=8
DEVNAME=sdf     DEVMAJOR=8
real    0m 0.09s
user    0m 0.03s
sys     0m 0.06s
tc@E310:~/rebuildfstab$
--- End code ---

I've attached the baseline file (findblockdevs) and the version with my changes (newfindblockdevs).
Lines beginning with  ###  were commented out by me.

curaga:
I worry about a potential race there - is it certain those devices (/the newest of them) exist when rebuildfstab is called. /sys gets populated early, but I don't remember when exactly udev creates devices wrt the called scripts.

No interest in the C approach :P

Rich:
Hi curaga
How do you feel about using  /proc/partitions? I can cut the time
by another factor of 2 parsing that source.

hiro:
7x faster, nice :D

maybe we should also replace blkid with a shellscript, then? /s

curaga:
/proc should be fine.

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