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authorTom Van Braeckel <tomvanbraeckel@gmail.com>2015-01-12 05:22:16 +0100
committerMiklos Szeredi <mszeredi@suse.cz>2015-03-19 15:29:22 +0100
commit94e4fe2cab3d43b3ba7c3f721743006a8c9d913a (patch)
treeb6bb327977ae0e4a1173ab32bb4f93f9b460e17e
parentaa991b3b267e24f578bac7b09cc57579b660304b (diff)
downloadlinux-sh-94e4fe2cab3d43b3ba7c3f721743006a8c9d913a.tar.gz
fuse: explicitly set /dev/fuse file's private_data
The misc subsystem (which is used for /dev/fuse) initializes private_data to point to the misc device when a driver has registered a custom open file operation, and initializes it to NULL when a custom open file operation has *not* been provided. This subtle quirk is confusing, to the point where kernel code registers *empty* file open operations to have private_data point to the misc device structure. And it leads to bugs, where the addition or removal of a custom open file operation surprisingly changes the initial contents of a file's private_data structure. So to simplify things in the misc subsystem, a patch [1] has been proposed to *always* set the private_data to point to the misc device, instead of only doing this when a custom open file operation has been registered. But before this patch can be applied we need to modify drivers that make the assumption that a misc device file's private_data is initialized to NULL because they didn't register a custom open file operation, so they don't rely on this assumption anymore. FUSE uses private_data to store the fuse_conn and errors out if this is not initialized to NULL at mount time. Hence, we now set a file's private_data to NULL explicitly, to be independent of whatever value the misc subsystem initializes it to by default. [1] https://lkml.org/lkml/2014/12/4/939 Reported-by: Giedrius Statkevicius <giedriuswork@gmail.com> Reported-by: Thierry Reding <thierry.reding@gmail.com> Signed-off-by: Tom Van Braeckel <tomvanbraeckel@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
-rw-r--r--fs/fuse/dev.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 71c4619af333..39706c57ad3c 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1353,6 +1353,17 @@ static ssize_t fuse_dev_do_read(struct fuse_conn *fc, struct file *file,
return err;
}
+static int fuse_dev_open(struct inode *inode, struct file *file)
+{
+ /*
+ * The fuse device's file's private_data is used to hold
+ * the fuse_conn(ection) when it is mounted, and is used to
+ * keep track of whether the file has been mounted already.
+ */
+ file->private_data = NULL;
+ return 0;
+}
+
static ssize_t fuse_dev_read(struct kiocb *iocb, const struct iovec *iov,
unsigned long nr_segs, loff_t pos)
{
@@ -2220,6 +2231,7 @@ static int fuse_dev_fasync(int fd, struct file *file, int on)
const struct file_operations fuse_dev_operations = {
.owner = THIS_MODULE,
+ .open = fuse_dev_open,
.llseek = no_llseek,
.read = do_sync_read,
.aio_read = fuse_dev_read,