Implement the FUSE passthrough ioctl() that associates the lower
(passthrough) file system 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 lower file system.
To enable the passthrough mode, userspace triggers 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 lower
file system file.
The value returned by the ioctl() to userspace can be:
- > 0: success, the identifier can be used as part of an open/create
reply.
- < 0: an error occurred.
The value 0 has been left unused for backward compatibility: the
fuse_open_out field that is used to pass the passthrough_fh back to the
kernel uses the same bits that were previously as struct padding,
zero-initialized in the common libfuse implementation. Removing the 0
value fixes the ambiguity between the case in which 0 corresponds to a
real passthrough_fh or a missing implementation, simplifying the
userspace implementation.
For the passthrough mode to be successfully activated, the lower file
system file must implement both read_ and write_iter file operations.
This extra check avoids special pseudo files to be targeted for this
feature.
Passthrough comes with another limitation: no further file system stacking
is allowed for those FUSE file systems using passthrough.
Signed-off-by: Alessio Balsini <balsini@xxxxxxxxxxx>
---
fs/fuse/inode.c | 5 +++
fs/fuse/passthrough.c | 80 +++++++++++++++++++++++++++++++++++++++++--
2 files changed, 83 insertions(+), 2 deletions(-)
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 6738dd5ff5d2..1e94c54d1455 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1034,6 +1034,11 @@ EXPORT_SYMBOL_GPL(fuse_send_init);
static int free_fuse_passthrough(int id, void *p, void *data)
{
+ struct fuse_passthrough *passthrough = (struct fuse_passthrough *)p;
+
+ fuse_passthrough_release(passthrough);
+ kfree(p);
+
return 0;
}
diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
index 594060c654f8..a135c955cc33 100644
--- a/fs/fuse/passthrough.c
+++ b/fs/fuse/passthrough.c
@@ -3,19 +3,95 @@
#include "fuse_i.h"
#include <linux/fuse.h>
+#include <linux/idr.h>
int fuse_passthrough_open(struct fuse_dev *fud,
struct fuse_passthrough_out *pto)
{
- return -EINVAL;
+ int res;
+ struct file *passthrough_filp;
+ struct fuse_conn *fc = fud->fc;
+ struct fuse_passthrough *passthrough;
+
+ if (!fc->passthrough)
+ return -EPERM;
+
+ /* This field is reserved for future implementation */
+ if (pto->len != 0)
+ return -EINVAL;
+
+ passthrough_filp = fget(pto->fd);
+ if (!passthrough_filp) {
+ pr_err("FUSE: invalid file descriptor for passthrough.\n");
+ return -EBADF;
+ }
+
+ if (!passthrough_filp->f_op->read_iter ||
+ !passthrough_filp->f_op->write_iter) {
+ pr_err("FUSE: passthrough file misses file operations.\n");
+ return -EBADF;
+ }
+
+ passthrough = kmalloc(sizeof(struct fuse_passthrough), GFP_KERNEL);
+ if (!passthrough)
+ return -ENOMEM;
+
+ passthrough->filp = passthrough_filp;
+
+ idr_preload(GFP_KERNEL);
+ spin_lock(&fc->passthrough_req_lock);
+ res = idr_alloc(&fc->passthrough_req, passthrough, 1, 0, GFP_ATOMIC);
+ spin_unlock(&fc->passthrough_req_lock);
+ idr_preload_end();
+ if (res <= 0) {
+ fuse_passthrough_release(passthrough);
+ kfree(passthrough);
+ }
+
+ return res;
}
int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff,
struct fuse_open_out *openarg)
{
- return -EINVAL;
+ struct inode *passthrough_inode;
+ struct super_block *passthrough_sb;
+ struct fuse_passthrough *passthrough;
+ int passthrough_fh = openarg->passthrough_fh;
+
+ if (!fc->passthrough)
+ return -EPERM;
+
+ /* Default case, passthrough is not requested */
+ if (passthrough_fh <= 0)
+ return -EINVAL;
+
+ spin_lock(&fc->passthrough_req_lock);
+ passthrough = idr_remove(&fc->passthrough_req, passthrough_fh);
+ spin_unlock(&fc->passthrough_req_lock);
+
+ if (!passthrough)
+ return -EINVAL;
+
+ passthrough_inode = file_inode(passthrough->filp);
+ passthrough_sb = passthrough_inode->i_sb;
+ if (passthrough_sb->s_stack_depth >= FILESYSTEM_MAX_STACK_DEPTH) {
+ pr_err("FUSE: fs stacking depth exceeded for passthrough\n");
+ fuse_passthrough_release(passthrough);
+ kfree(passthrough);
+ return -EINVAL;
+ }
+
+ ff->passthrough = *passthrough;
+ kfree(passthrough);
+
+ return 0;
}
void fuse_passthrough_release(struct fuse_passthrough *passthrough)
{
+ if (passthrough->filp) {
+ fput(passthrough->filp);
+ passthrough->filp = NULL;
+ }
}
--
2.29.0.rc1.297.gfa9743e501-goog
