usb: gadget: f_mass_storage: forced_eject attribute

PATCH Superseded Maxim Devaev 3 participants 4 messages Jul 7, 2022 – Jul 10, 2022

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Maxim Devaev

author

2022-07-07 17:09 UTC #0 lore raw

PATCH v3 1/1 usb: gadget: f_mass_storage: forced_eject attribute

It allows to reset prevent_medium_removal flag and "eject" the image.

The patch is a completely alternative implementation of the previously proposed [1], the idea of which was born after the mentioned discussion.

Signed-off-by Maxim Devaev <[email protected]>

Link https://lore.kernel.org/lkml/[email protected] [1] open here

---
 .../testing/configfs-usb-gadget-mass-storage  |  6 +++++
 Documentation/usb/gadget-testing.rst          |  6 +++++
 Documentation/usb/mass-storage.rst            |  9 +++++++
 drivers/usb/gadget/function/f_mass_storage.c  | 25 +++++++++++++++++++
 drivers/usb/gadget/function/storage_common.c  | 11 ++++++++
 drivers/usb/gadget/function/storage_common.h  |  2 ++
 6 files changed, 59 insertions(+)

Documentation/ABI/testing/configfs-usb-gadget-mass-storage +6 -0

index c86b63a7bb43..d899adb57e81 100644
@@ -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

index c18113077889..15624c4fe633 100644
@@ -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

index d181b47c3cb6..f399ec631599 100644
@@ -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

index 6ad669dde41c..00cac2a38178 100644
@@ -2520,10 +2520,21 @@ 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 ******************************/

@@ -2677,6 +2688,7 @@ 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
 };

@@ -3090,6 +3102,18 @@ 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,

@@ -3097,6 +3121,7 @@ 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 +11 -0

index b859a158a414..8cd95bf7831f 100644
@@ -519,4 +519,15 @@ 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;
+
+	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");

drivers/usb/gadget/function/storage_common.h +2 -0

index bdeb1e233fc9..0a544a82cbf8 100644
@@ -219,5 +219,7 @@ ssize_t fsg_store_removable(struct fsg_lun *curlun, const char *buf,
 			    size_t count);
 ssize_t fsg_store_inquiry_string(struct fsg_lun *curlun, const char *buf,
 				 size_t count);
+ssize_t fsg_store_forced_eject(struct fsg_lun *curlun, struct rw_semaphore *filesem,
+			       const char *buf, size_t count);
 
 #endif /* USB_STORAGE_COMMON_H */

Signature · 1 line

2.37.0

Alan Stern

Reviewed-by on v3 1/1

2022-07-07 17:23 UTC #1 lore raw

Quoted 8 lines · Maxim Devaev

It allows to reset prevent_medium_removal flag and "eject" the image.
The patch is a completely alternative implementation of the previously proposed [1], the idea of which was born after the mentioned discussion.
Signed-off-by Maxim Devaev <[email protected]>
Link https://lore.kernel.org/lkml/[email protected] [1] open here
---

Greg's patch bot is going to complain that you didn't describe the differences between v2 and v3 at this point.

And since you'll have to submit the patch again...

drivers/usb/gadget/function/storage_common.c ssize_t fsg_store_inquiry_string(struct fsg_lun *curlun, const char *buf, · line 526

Quoted 5 lines

drivers/usb/gadget/function/storage_common.c +5 -0

+ssize_t fsg_store_forced_eject(struct fsg_lun *curlun, struct rw_semaphore *filesem,
+			       const char *buf, size_t count)
+{
+	int ret;
+

... How about putting a comment line here, explaining that this override will cause the medium to be ejected no matter what the host wants?

drivers/usb/gadget/function/storage_common.c ssize_t fsg_store_inquiry_string(struct fsg_lun *curlun, const char *buf, · line 531

Quoted 5 lines

drivers/usb/gadget/function/storage_common.c +5 -0

+	curlun->prevent_medium_removal = 0;
+	ret = fsg_store_file(curlun, filesem, "", 0);
+	return ret < 0 ? ret : count;
+}
+EXPORT_SYMBOL_GPL(fsg_store_forced_eject);

In any case, in the next submission you can add:

Reviewed-by Alan Stern <[email protected]>

Alan Stern

Maxim Devaev

author

2022-07-10 20:19 UTC #2 lore raw

В Thu, 7 Jul 2022 13:23:50 -0400

Quoted 2 lines · Alan Stern

Greg's patch bot is going to complain that you didn't describe the differences between v2 and v3 at this point.

Fixed

Quoted 3 lines

... How about putting a comment line here, explaining that this override will cause the medium to be ejected no matter what the host wants?

Yep, I've added.

Quoted 1 line

Reviewed-by Alan Stern <[email protected]>

Added, thank you! Submitted v4.

This is the friendly patch-bot of Greg Kroah-Hartman. You have sent him a patch that has triggered this response. He used to manually respond to these common problems, but in order to save his sanity (he kept writing the same thing over and over, yet to different people), I was created. Hopefully you will not take offence and will fix the problem in your patch and resubmit it so that it can be accepted into the Linux kernel tree.

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