On 2/24/12, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> You haven't said what you need.
>
> For example, suppose you're running an older kernel, and your init
> script finds a bunch of USB devices and then exits. At that moment you
> plug in a USB flash drive. Clearly the script will not have been able
> to find it. How do you deal with that?
>
> There's still more to this. The "scan complete" message you mentioned
> earlier gets printed when the SCSI layer has been told to scan the
> device. But the SCSI layer can perform its scanning asynchronously,
> and in particular, SCSI disks are always registered asynchronously.
> Therefore the "scan complete" message doesn't mean that the attached
> device has been fully scanned.
>
Yes I have said what I need. The 'init' script finds drives present at
bootup. Any USB drive, usually when Puppy is booting off that drive,
will be present.
As I said, udev is used after switch_root, and anything plugged in
after bootup is handled.
I remember looking at another tiny Linux with a small initramfs that
also did not use udev (or any variant) in the initramfs, and they just
put in a big "sleep" to wait for, hopefully, the slowest USB drives.
We wait until all USB drives are reported as found, and the "scan
complete" for all of them. What we found is that the drives are
discovered fairly promptly, but we have a suitable sleep to make sure
all are found, then wait for the "scan complete" messages, but then
wait for the drives to become ready.
It works 100% on a huge range of hardware. If you are curious, here is
the code. This runs as a parallel process to the main 'init' script:
USBSTORAGES=0 ; CNTUSB=0
while [ $USBSTORAGES -eq 0 ];do
sleep 1
echo -n "." > /dev/console
CNTUSB=$(($CNTUSB+1))
[ $CNTUSB -gt 5 ] && break
#v412 bug, ubuntu kernel, got duplicate 'device found at 2', need 'sort -u'...
USBSTORAGES=`/bin/dmesg | grep "usb-storage: device found at" | sort
-u | wc -l`
[ $USBSTORAGES -eq 0 ] && break
AVAILABLEUSBSTORAGES=`/bin/dmesg | grep "usb-storage: device scan
complete" | wc -l`
[ $USBSTORAGES -ne $AVAILABLEUSBSTORAGES ] && USBSTORAGES=0
done
#i want this to work with kernel that does not have my usb-storage
patch, feedback is that 3 secs is enough...
while [ $CNTUSB -lt 3 ];do
sleep 1
CNTUSB=$(($CNTUSB+1))
echo -en "\\033[1;33m.\\033[0;39m" >/dev/console #yellow dot
done
#wait for usb partitions to become available...
#entries in /sys/block show up, but ex /sys/block/sda/sda1 takes a bit longer...
#note, if usb card-reader plugged in but no cards inserted, this will timeout...
#note, will also timeout if usb optical drive (sr), but ok, they need
extra time...
ALLUSBDRVS="`find /sys/block -maxdepth 1 -name 'sd*' -o -name 'sr*' |
xargs -l readlink 2>/dev/null | grep '/usb[0-9]' | rev | cut -f 1 -d
'/' | rev | tr '\n' ' '`"
[ "$ALLUSBDRVS" = " " ] && ALLUSBDRVS=""
for ONEDRV in $ALLUSBDRVS
do
while [ ! -e /sys/block/${ONEDRV}/${ONEDRV}1 ];do
sleep 1
echo -en "\\033[1;31m.\\033[0;39m" >/dev/console #red dot
CNTUSB=$(($CNTUSB+1))
[ $CNTUSB -gt 6 ] && break
done
#force update of /proc/partitions...
dd if=/dev/${ONEDRV} of=/dev/null bs=512 count=1 >/dev/null 2>&1
done
Regards,
Barry Kauler
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