Hi, The appended patch contains a warning about the possiblity to lose data if any filesystems on USB devices are mounted before suspend. The A:-Q: part is from my correspondence with Alan Stern (thanks Alan). Greetings, Rafael Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx> --- Documentation/power/swsusp.txt | 24 ++++++++++++++++++++++++ 1 files changed, 24 insertions(+) Index: linux-2.6.16-rc3-mm1/Documentation/power/swsusp.txt =================================================================== --- linux-2.6.16-rc3-mm1.orig/Documentation/power/swsusp.txt +++ linux-2.6.16-rc3-mm1/Documentation/power/swsusp.txt @@ -17,6 +17,11 @@ Some warnings, first. * but it will probably only crash. * * (*) suspend/resume support is needed to make it safe. + * + * If you have any filesystems on USB devices mounted before suspend, + * they won't be mounted after resume and you may lose data, as though + * you have unplugged the USB devices with mounted filesystems on them + * (see the FAQ below for details). You need to append resume=/dev/your_swap_partition to kernel command line. Then you suspend by @@ -347,3 +352,22 @@ terminal the kernel switches to during s kernel console loglevel to at least 5, for example by doing echo 5 > /proc/sys/kernel/printk + +Q: Is this true that if I have a mounted filesystem on a USB device and +I suspend to disk, I can lose data unless the filesystem has been mounted +with "sync"? + +A: That's right. It depends on your hardware, and it could be true even for +suspend-to-RAM. In fact, even with "-o sync" you can lose data if your +programs have information in buffers they haven't written out to disk. + +If you're lucky, your hardware will support low-power modes for USB +controllers while the system is asleep. Lots of hardware doesn't, +however. Shutting off the power to a USB controller is equivalent to +unplugging all the attached devices. + +Remember that it's always a bad idea to unplug a disk drive containing a +mounted filesystem. With USB that's true even when your system is asleep! +The safest thing is to unmount all USB-based filesystems before suspending +and remount them after resuming. +
