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usb: gadget: f_mass_storage: forced_eject attribute

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It allows to reset prevent_medium_removal flag and "eject" the image.
This can be useful to free the drive from a hunging host or if the host
continues to use the drive even after unmounting (Linux does this).
It's also a bit like using an unfolded paperclip on an optical drive.

Previously, the undocumented method of sending SIGUSR1 to a special
"file-storage" kernel thread could be used for these purposes,
but when using multiple storages there was no way to distinguish
one from the other, so we had to send a signal to everyone.

Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Maxim Devaev <mdevaev@gmail.com>
Link: https://lore.kernel.org/r/20220711102956.19642-1-mdevaev@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Maxim Devaev
2022-07-11 13:29:57 +03:00
committed by Greg Kroah-Hartman
parent 8097cf2fb3
commit 421c8d9a20
6 changed files with 63 additions and 0 deletions
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6
Documentation/ABI/testing/configfs-usb-gadget-mass-storage
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@@ -32,4 +32,10 @@ Description:
being a CD-ROM.
nofua Flag specifying that FUA flag
in SCSI WRITE(10,12)
forced_eject This write-only file is useful only when
the function is active. It causes the backing
file to be forcibly detached from the LUN,
regardless of whether the host has allowed it.
Any non-zero number of bytes written will
result in ejection.
=========== ==============================================