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From: Alessio Balsini <balsini@android.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Akilesh Kailash <akailash@google.com>,
	Amir Goldstein <amir73il@gmail.com>,
	Antonio SJ Musumeci <trapexit@spawn.link>,
	David Anderson <dvander@google.com>,
	Giuseppe Scrivano <gscrivan@redhat.com>,
	Jann Horn <jannh@google.com>, Jens Axboe <axboe@kernel.dk>,
	Martijn Coenen <maco@android.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Lawrence <paullawrence@google.com>,
	Stefano Duo <duostefano93@gmail.com>,
	Zimuzo Ezeozue <zezeozue@google.com>,
	fuse-devel@lists.sourceforge.net, kernel-team@android.com,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH V10 2/5] fuse: Passthrough initialization and release
Date: Mon, 26 Oct 2020 12:50:13 +0000
Message-ID: <20201026125016.1905945-3-balsini@android.com> (raw)
In-Reply-To: <20201026125016.1905945-1-balsini@android.com>

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@android.com>
---
 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


  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-26 12:50 [PATCH V10 0/5] fuse: Add support for passthrough read/write Alessio Balsini
2020-10-26 12:50 ` [PATCH V10 1/5] fuse: Definitions and ioctl() for passthrough Alessio Balsini
2020-10-26 12:50 ` Alessio Balsini [this message]
2020-11-26 13:33   ` [PATCH V10 2/5] fuse: Passthrough initialization and release Peng Tao
2020-11-27 13:41     ` Alessio Balsini
2020-11-28  1:57       ` Peng Tao
2020-12-16 16:46         ` Alessio Balsini
     [not found]   ` <3bf58b6f-c7eb-7baa-384d-ae0830d8bceb@tcl.com>
2020-12-16 16:55     ` Alessio Balsini
2020-10-26 12:50 ` [PATCH V10 3/5] fuse: Introduce synchronous read and write for passthrough Alessio Balsini
2020-10-26 12:50 ` [PATCH V10 4/5] fuse: Handle asynchronous read and write in passthrough Alessio Balsini
2020-10-26 12:50 ` [PATCH V10 5/5] fuse: Use daemon creds in passthrough mode Alessio Balsini
2020-11-28  2:10 ` [PATCH V10 0/5] fuse: Add support for passthrough read/write Peng Tao
2020-11-30 11:08   ` Alessio Balsini

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