linux-kernel - [PATCH] [g_mass_storage] Fix unmount problem with OS-X

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Message-Id: <1337158489-27142-1-git-send-email-panto@antoniou-consulting.com>
Date:	Wed, 16 May 2012 08:54:49 +0000
From:	Pantelis Antoniou <panto@...oniou-consulting.com>
To:	Russ.Dill@...com, linux-kernel@...r.kernel.org
Cc:	Pantelis Antoniou <panto@...oniou-consulting.com>
Subject: [PATCH] [g_mass_storage] Fix unmount problem with OS-X

OS-X uses a sequence on unmounting that makes us close the backing
file. Apparently there's no way to open it again, which makes it
impossible to remount without rmmod'ing g_mass_storage.

Fix this by adding a media_ejected flag to each lun, and keeping
track of it properly.

Any other method (i.e. preventing unmount, and not keeping track
of the eject status) failed due to OS-X sending start stop commands
after the unmount and checking again.
---
 drivers/usb/gadget/f_mass_storage.c |   21 ++++++++++++++-------
 drivers/usb/gadget/storage_common.c |   11 +++++++++++
 2 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
index cb8c162..b865d20 100644
--- a/drivers/usb/gadget/f_mass_storage.c
+++ b/drivers/usb/gadget/f_mass_storage.c
@@ -1445,6 +1445,9 @@ static int do_start_stop(struct fsg_common *common)
 			curlun->sense_data = SS_MEDIUM_NOT_PRESENT;
 			return -EINVAL;
 		}
+
+		/* if the host is trying again, the media are mounted */
+		fsg_lun_set_ejected(curlun, 0);
 		return 0;
 	}
 
@@ -1468,11 +1471,15 @@ static int do_start_stop(struct fsg_common *common)
 			return 0;
 	}
 
-	up_read(&common->filesem);
-	down_write(&common->filesem);
-	fsg_lun_close(curlun);
-	up_write(&common->filesem);
-	down_read(&common->filesem);
+	/*
+	 * Do not close the LUNs, just made them invisible.
+	 * When the next exception comes we make them visible
+	 * again. This fixes the bug where MacOSX unmounts
+	 * and then it's impossible to mount again, since
+	 * fsg_lun_open is never called again.
+	 */
+
+	fsg_lun_set_ejected(curlun, 1);
 
 	return common->ops && common->ops->post_eject
 		? min(0, common->ops->post_eject(common, curlun,
@@ -1531,7 +1538,6 @@ static int do_mode_select(struct fsg_common *common, struct fsg_buffhd *bh)
 	return -EINVAL;
 }
 
-
 /*-------------------------------------------------------------------------*/
 
 static int halt_bulk_in_endpoint(struct fsg_dev *fsg)
@@ -1917,7 +1923,7 @@ static int check_command(struct fsg_common *common, int cmnd_size,
 
 	/* If the medium isn't mounted and the command needs to access
 	 * it, return an error. */
-	if (curlun && !fsg_lun_is_open(curlun) && needs_medium) {
+	if (curlun && !fsg_lun_is_open_and_mounted(curlun) && needs_medium) {
 		curlun->sense_data = SS_MEDIUM_NOT_PRESENT;
 		return -EINVAL;
 	}
@@ -2533,6 +2539,7 @@ static void handle_exception(struct fsg_common *common)
 			curlun->unit_attention_data = SS_NO_SENSE;
 			curlun->sense_data_info = 0;
 			curlun->info_valid = 0;
+			curlun->media_ejected = 0;
 		}
 		common->state = FSG_STATE_IDLE;
 	}
diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c
index 8081ca3..723c6aa 100644
--- a/drivers/usb/gadget/storage_common.c
+++ b/drivers/usb/gadget/storage_common.c
@@ -199,6 +199,7 @@ struct fsg_lun {
 	unsigned int	registered:1;
 	unsigned int	info_valid:1;
 	unsigned int	nofua:1;
+	unsigned int	media_ejected:1;
 
 	u32		sense_data;
 	u32		sense_data_info;
@@ -211,6 +212,16 @@ struct fsg_lun {
 
 #define fsg_lun_is_open(curlun)	((curlun)->filp != NULL)
 
+#define fsg_lun_is_ejected(curlun) ((curlun)->media_ejected)
+
+#define fsg_lun_set_ejected(curlun, v) ((curlun)->media_ejected = !!(v))
+
+#define fsg_lun_is_open_and_mounted(curlun) \
+	({ \
+		const struct fsg_lun *_curlun = (curlun); \
+		fsg_lun_is_open(_curlun) && !fsg_lun_is_ejected(_curlun); \
+	 })
+
 static struct fsg_lun *fsg_lun_from_dev(struct device *dev)
 {
 	return container_of(dev, struct fsg_lun, dev);
-- 
1.7.1

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