Commit 421c8d9a authored by Maxim Devaev's avatar Maxim Devaev Committed by Greg Kroah-Hartman
Browse files

usb: gadget: f_mass_storage: forced_eject attribute 



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: default avatarAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: default avatarMaxim Devaev <mdevaev@gmail.com>
Link: https://lore.kernel.org/r/20220711102956.19642-1-mdevaev@gmail.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 8097cf2f

Documentation/ABI/testing/configfs-usb-gadget-mass-storage

+6 −0
Original line number Diff line number Diff line
@@ -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.

		===========	==============================================

Documentation/usb/gadget-testing.rst

+6 −0
Original line number Diff line number Diff line
@@ -333,6 +333,12 @@ In each lun directory there are the following attribute files: 
			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.

	=============== ==============================================



Testing the MASS STORAGE function

Documentation/usb/mass-storage.rst

+9 −0
Original line number Diff line number Diff line
@@ -181,6 +181,15 @@ sysfs entries 
    Reflects the state of nofua flag for given logical unit.  It can

    be read and written.



  - forced_eject



    When written into, it causes the backing file to be forcibly

    detached from the LUN, regardless of whether the host has allowed

    it.  The content doesn't matter, any non-zero number of bytes

    written will result in ejection.



    Can not be read.



  Other then those, as usual, the values of module parameters can be

  read from /sys/module/g_mass_storage/parameters/* files.

drivers/usb/gadget/function/f_mass_storage.c

+25 −0
Original line number Diff line number Diff line
@@ -2651,10 +2651,21 @@ static ssize_t file_store(struct device *dev, struct device_attribute *attr, 
	return fsg_store_file(curlun, filesem, buf, count);

}



static ssize_t forced_eject_store(struct device *dev,

				  struct device_attribute *attr,

				  const char *buf, size_t count)

{

	struct fsg_lun		*curlun = fsg_lun_from_dev(dev);

	struct rw_semaphore	*filesem = dev_get_drvdata(dev);



	return fsg_store_forced_eject(curlun, filesem, buf, count);

}



static DEVICE_ATTR_RW(nofua);

/* mode wil be set in fsg_lun_attr_is_visible() */

static DEVICE_ATTR(ro, 0, ro_show, ro_store);

static DEVICE_ATTR(file, 0, file_show, file_store);

static DEVICE_ATTR_WO(forced_eject);



/****************************** FSG COMMON ******************************/
@@ -2808,6 +2819,7 @@ static struct attribute *fsg_lun_dev_attrs[] = { 
	&dev_attr_ro.attr,

	&dev_attr_file.attr,

	&dev_attr_nofua.attr,

	&dev_attr_forced_eject.attr,

	NULL

};
@@ -3221,6 +3233,18 @@ static ssize_t fsg_lun_opts_inquiry_string_store(struct config_item *item, 


CONFIGFS_ATTR(fsg_lun_opts_, inquiry_string);



static ssize_t fsg_lun_opts_forced_eject_store(struct config_item *item,

					       const char *page, size_t len)

{

	struct fsg_lun_opts *opts = to_fsg_lun_opts(item);

	struct fsg_opts *fsg_opts = to_fsg_opts(opts->group.cg_item.ci_parent);



	return fsg_store_forced_eject(opts->lun, &fsg_opts->common->filesem,

				      page, len);

}



CONFIGFS_ATTR_WO(fsg_lun_opts_, forced_eject);



static struct configfs_attribute *fsg_lun_attrs[] = {

	&fsg_lun_opts_attr_file,

	&fsg_lun_opts_attr_ro,
@@ -3228,6 +3252,7 @@ static struct configfs_attribute *fsg_lun_attrs[] = { 
	&fsg_lun_opts_attr_cdrom,

	&fsg_lun_opts_attr_nofua,

	&fsg_lun_opts_attr_inquiry_string,

	&fsg_lun_opts_attr_forced_eject,

	NULL,

};

drivers/usb/gadget/function/storage_common.c

+15 −0
Original line number Diff line number Diff line
@@ -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");