Warn in the documentation that data may be lost if there are some filesystems
mounted from USB devices before suspend.
[Thanks to Alan Stern for providing the answer to the question in the Q:-A: part.]
Signed-off-by: Rafael J. Wysocki <[email protected]>
Acked-by: Pavel Machek <[email protected]>
---
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.
+
-
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