Implement the FUSE passthrough ioctl that associates a backing
(passthrough) file with the fuse_file.
The file descriptor passed to the ioctl by the FUSE daemon is used to
access the relative file pointer, that will be copied to the fuse_file
data structure to consolidate the link between the FUSE and the backing
file.
To enable the passthrough mode, FUSE daemon calls the
FUSE_DEV_IOC_PASSTHROUGH_OPEN ioctl and, if the call succeeds, receives
back an identifier that will be used at open/create response time in the
fuse_open_out field to associate the FUSE file to the backing file.
The value returned by the ioctl to user space can be:
> 0: success, the value can be used as part of an open/create reply.
<= 0: an error occurred.
== 0: represents an error to preserve backward compatibility - the
fuse_open_out field that is used to pass the backing_id back to the
kernel uses the same bits that were previously as struct padding, and is
commonly zero-initialized (e.g., in the libfuse implementation).
Removing 0 from the correct values fixes the ambiguity between the case
in which 0 corresponds to a real backing_id, a missing implementation
of FUSE passthrough or a request for a normal FUSE file, simplifying the
user space implementation.
For the passthrough mode to be successfully activated, the backing file
filesystem must implement both read_iter and write_iter file operations.
This extra check avoids special pseudo files to be used for passhrough.
Passthrough comes with another limitation: no further filesystem stacking
is allowed for those FUSE filesystems using passthrough.
The FUSE daemon must call FUSE_DEV_IOC_PASSTHROUGH_CLOSE ioctl to drop
the reference on the backing file. This can be done immediattely after
responding to open or at a later time.
In any case, the backing file will be kept open by the FUSE driver until
the last fuse_file that was setup to passthrough to that backing file is
closed AND the FUSE_DEV_IOC_PASSTHROUGH_CLOSE ioctl was called.
Signed-off-by: Alessio Balsini <balsini@xxxxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/fuse/fuse_i.h | 1 +
fs/fuse/inode.c | 1 +
fs/fuse/passthrough.c | 89 +++++++++++++++++++++++++++++++++++++++++--
3 files changed, 87 insertions(+), 4 deletions(-)
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index f52604534ff6..9ad1cc37a5c4 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -181,6 +181,7 @@ struct fuse_passthrough {
/** refcount */
refcount_t count;
+ struct rcu_head rcu;
};
/** FUSE specific file data */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 271586fac008..4200fb13883e 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1301,6 +1301,7 @@ static int fuse_passthrough_id_free(int id, void *p, void *data)
WARN_ON_ONCE(refcount_read(&passthrough->count) != 1);
fuse_passthrough_free(passthrough);
+
return 0;
}
diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
index fc723e004de9..8d090ae252f2 100644
--- a/fs/fuse/passthrough.c
+++ b/fs/fuse/passthrough.c
@@ -3,6 +3,7 @@
#include "fuse_i.h"
#include <linux/file.h>
+#include <linux/idr.h>
/*
* Returns passthrough_fh id that can be passed with FOPEN_PASSTHROUGH
@@ -10,18 +11,98 @@
*/
int fuse_passthrough_open(struct fuse_conn *fc, int backing_fd)
{
- return -EINVAL;
+ struct file *passthrough_filp;
+ struct inode *passthrough_inode;
+ struct super_block *passthrough_sb;
+ struct fuse_passthrough *passthrough;
+ int res;
+
+ if (!fc->passthrough)
+ return -EPERM;
+
+ passthrough_filp = fget(backing_fd);
+ if (!passthrough_filp)
+ return -EBADF;
+
+ res = -EOPNOTSUPP;
+ if (!passthrough_filp->f_op->read_iter ||
+ !passthrough_filp->f_op->write_iter)
+ goto out_fput;
+
+ passthrough_inode = file_inode(passthrough_filp);
+ passthrough_sb = passthrough_inode->i_sb;
+ res = -ELOOP;
+ if (passthrough_sb->s_stack_depth >= FILESYSTEM_MAX_STACK_DEPTH)
+ goto out_fput;
+
+ passthrough = kmalloc(sizeof(struct fuse_passthrough), GFP_KERNEL);
+ res = -ENOMEM;
+ if (!passthrough)
+ goto out_fput;
+
+ passthrough->filp = passthrough_filp;
+ refcount_set(&passthrough->count, 1);
+
+ idr_preload(GFP_KERNEL);
+ spin_lock(&fc->lock);
+ res = idr_alloc_cyclic(&fc->passthrough_files_map, passthrough, 1, 0,
+ GFP_ATOMIC);
+ spin_unlock(&fc->lock);
+ idr_preload_end();
+
+ if (res < 0)
+ fuse_passthrough_free(passthrough);
+
+ return res;
+
+out_fput:
+ fput(passthrough_filp);
+
+ return res;
}
int fuse_passthrough_close(struct fuse_conn *fc, int passthrough_fh)
{
- return -EINVAL;
+ struct fuse_passthrough *passthrough;
+
+ if (!fc->passthrough)
+ return -EPERM;
+
+ if (passthrough_fh <= 0)
+ return -EINVAL;
+
+ spin_lock(&fc->lock);
+ passthrough = idr_remove(&fc->passthrough_files_map, passthrough_fh);
+ spin_unlock(&fc->lock);
+
+ if (!passthrough)
+ return -ENOENT;
+
+ fuse_passthrough_put(passthrough);
+
+ return 0;
}
int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff,
struct fuse_open_out *openarg)
{
- return -EINVAL;
+ int passthrough_fh = openarg->passthrough_fh;
+ struct fuse_passthrough *passthrough;
+
+ if (passthrough_fh <= 0)
+ return -EINVAL;
+
+ rcu_read_lock();
+ passthrough = idr_find(&fc->passthrough_files_map, passthrough_fh);
+ if (passthrough && !refcount_inc_not_zero(&passthrough->count))
+ passthrough = NULL;
+ rcu_read_unlock();
+ if (!passthrough)
+ return -ENOENT;
+
+ ff->passthrough = passthrough;
+
+ return 0;
}
void fuse_passthrough_put(struct fuse_passthrough *passthrough)
@@ -36,5 +117,5 @@ void fuse_passthrough_free(struct fuse_passthrough *passthrough)
fput(passthrough->filp);
passthrough->filp = NULL;
}
- kfree(passthrough);
+ kfree_rcu(passthrough, rcu);
}
--
2.34.1
