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Matthias reports that the Amazon Kindle automatically removes its emulated media if it doesn't receive another SCSI command within about one second after a SYNCHRONIZE CACHE. It does so even when the host has sent a PREVENT MEDIUM REMOVAL command. The reason for this behavior isn't clear, although it's not hard to make some guesses. At any rate, the results can be unexpected for anyone who tries to access the Kindle in an unusual fashion, and in theory they can lead to data loss (for example, if one file is closed and synchronized while other files are still in the middle of being written). To avoid such problems, this patch creates a new usb-storage quirks flag telling the driver always to issue a REQUEST SENSE following a SYNCHRONIZE CACHE command, and adds an unusual_devs entry for the Kindle with the flag set. This is sufficient to prevent the Kindle from doing its automatic unload, without interfering with proper operation. Another possible way to deal with this would be to increase the frequency of TEST UNIT READY polling that the kernel normally carries out for removable-media storage devices. However that would increase the overall load on the system and it is not as reliable, because the user can override the polling interval. Changing the driver's behavior is safer and has minimal overhead. CC: <stable@vger.kernel.org> Reported-and-tested-by: Matthias Schwarzott <zzam@gentoo.org> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Link: https://lore.kernel.org/r/20210317190654.GA497856@rowland.harvard.edu Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| usb-skeleton.c | ||