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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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15
drivers/usb/gadget/function/storage_common.c
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@@ -519,4 +519,19 @@ ssize_t fsg_store_inquiry_string(struct fsg_lun *curlun, const char *buf,
}
EXPORT_SYMBOL_GPL(fsg_store_inquiry_string);
ssize_t fsg_store_forced_eject(struct fsg_lun *curlun, struct rw_semaphore *filesem,
const char *buf, size_t count)
{
int ret;
/*
* Forcibly detach the backing file from the LUN
* regardless of whether the host has allowed it.
*/
curlun->prevent_medium_removal = 0;
ret = fsg_store_file(curlun, filesem, "", 0);
return ret < 0 ? ret : count;
}
EXPORT_SYMBOL_GPL(fsg_store_forced_eject);
MODULE_LICENSE("GPL");