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Message-Id: <20220711102956.19642-1-mdevaev@gmail.com>
Date: Mon, 11 Jul 2022 13:29:57 +0300
From: Maxim Devaev <mdevaev@...il.com>
To: linux-usb@...r.kernel.org
Cc: mdevaev@...il.com, stern@...land.harvard.edu,
gregkh@...uxfoundation.org, corbet@....net, balbi@...nel.org,
caihuoqing@...du.com, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org
Subject: [PATCH v5] 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: Alan Stern <stern@...land.harvard.edu>
Signed-off-by: Maxim Devaev <mdevaev@...il.com>
---
v4 -> v5: A more detailed description of the commit
v3 -> v4: Added comment for fsg_store_forced_eject() internals
v2 -> v3: Improved spelling
v1 -> v2: Added documentation for the ABI and sysfs
.../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 | 15 +++++++++++
drivers/usb/gadget/function/storage_common.h | 2 ++
6 files changed, 63 insertions(+)
diff --git a/Documentation/ABI/testing/configfs-usb-gadget-mass-storage b/Documentation/ABI/testing/configfs-usb-gadget-mass-storage
index c86b63a7bb43..d899adb57e81 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-mass-storage
+++ b/Documentation/ABI/testing/configfs-usb-gadget-mass-storage
@@ -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.
=========== ==============================================
diff --git a/Documentation/usb/gadget-testing.rst b/Documentation/usb/gadget-testing.rst
index c18113077889..15624c4fe633 100644
--- a/Documentation/usb/gadget-testing.rst
+++ b/Documentation/usb/gadget-testing.rst
@@ -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
diff --git a/Documentation/usb/mass-storage.rst b/Documentation/usb/mass-storage.rst
index d181b47c3cb6..f399ec631599 100644
--- a/Documentation/usb/mass-storage.rst
+++ b/Documentation/usb/mass-storage.rst
@@ -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.
diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
index 6ad669dde41c..00cac2a38178 100644
--- a/drivers/usb/gadget/function/f_mass_storage.c
+++ b/drivers/usb/gadget/function/f_mass_storage.c
@@ -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,
};
diff --git a/drivers/usb/gadget/function/storage_common.c b/drivers/usb/gadget/function/storage_common.c
index b859a158a414..03035dbbe97b 100644
--- a/drivers/usb/gadget/function/storage_common.c
+++ b/drivers/usb/gadget/function/storage_common.c
@@ -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");
diff --git a/drivers/usb/gadget/function/storage_common.h b/drivers/usb/gadget/function/storage_common.h
index bdeb1e233fc9..0a544a82cbf8 100644
--- a/drivers/usb/gadget/function/storage_common.h
+++ b/drivers/usb/gadget/function/storage_common.h
@@ -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 */
--
2.37.0
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