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FROMLIST: fuse: Introduce synchronous read and write for passthrough

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All the read and write operations performed on fuse_files which have the
passthrough feature enabled are forwarded to the associated lower file
system file via VFS.

Sending the request directly to the lower file system avoids the
userspace round-trip that, because of possible context switches and
additional operations might reduce the overall performance, especially
in those cases where caching doesn't help, for example in reads at
random offsets.

Verifying if a fuse_file has a lower file system file associated with
can be done by checking the validity of its passthrough_filp pointer.
This pointer is not NULL only if passthrough has been successfully
enabled via the appropriate ioctl().
When a read/write operation is requested for a FUSE file with
passthrough enabled, a new equivalent VFS request is generated, which
instead targets the lower file system file.
The VFS layer performs additional checks that allow for safer operations
but may cause the operation to fail if the process accessing the FUSE
file system does not have access to the lower file system.

This change only implements synchronous requests in passthrough,
returning an error in the case of asynchronous operations, yet covering
the majority of the use cases.

Bug: 179164095
Link: https://lore.kernel.org/lkml/20210125153057.3623715-6-balsini@android.com/
Signed-off-by: Alessio Balsini <balsini@android.com>
Change-Id: Ifbe6a247fe7338f87d078fde923f0252eeaeb668
Signed-off-by: Alessio Balsini <balsini@google.com>
(cherry picked from commit ea9685a7f9cb16b30e25386386274fdd30627c3a)
Signed-off-by: alk3pInjection <webmaster@raspii.tech>
Signed-off-by: atndko <z1281552865@gmail.com>
Signed-off-by: Zlatan Radovanovic <zlatan.radovanovic@fet.ba>
Signed-off-by: Cyber Knight <cyberknight755@gmail.com>
Signed-off-by: Forenche <prahul2003@gmail.com>
This commit is contained in:
Alessio Balsini 2021-01-25 17:03:31 +00:00 committed by Forenche
parent 1e1a29d856
commit 67472bb21d
No known key found for this signature in database
GPG Key ID: 1337D655BAFE85E2
3 changed files with 66 additions and 0 deletions
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7
fs/fuse/file.c
View File

@ -983,6 +983,7 @@ static ssize_t fuse_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
struct fuse_file *ff = iocb->ki_filp->private_data;
ssize_t ret_val;
#endif /* CONFIG_FUSE_FS_SHORTCIRCUIT */
struct fuse_file *ff = iocb->ki_filp->private_data;
/*
* In auto invalidate mode, always update attributes on read.
@ -1004,6 +1005,8 @@ static ssize_t fuse_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
return ret_val;
#else
if (ff->passthrough.filp)
return fuse_passthrough_read_iter(iocb, to);
return generic_file_read_iter(iocb, to);
#endif /* CONFIG_FUSE_FS_SHORTCIRCUIT */
}
@ -1251,6 +1254,10 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
struct inode *inode = mapping->host;
ssize_t err;
loff_t endbyte = 0;
struct fuse_file *ff = file->private_data;
if (ff->passthrough.filp)
return fuse_passthrough_write_iter(iocb, from);
#ifdef CONFIG_FUSE_FS_SHORTCIRCUIT
if (ff && ff->rw_lower_file) {

2
fs/fuse/fuse_i.h
View File

@ -1045,5 +1045,7 @@ int fuse_passthrough_open(struct fuse_dev *fud,
int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff,
struct fuse_open_out *openarg);
void fuse_passthrough_release(struct fuse_passthrough *passthrough);
ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *to);
ssize_t fuse_passthrough_write_iter(struct kiocb *iocb, struct iov_iter *from);
#endif /* _FS_FUSE_I_H */

57
fs/fuse/passthrough.c
View File

@ -5,6 +5,63 @@
#include <linux/file.h>
#include <linux/fuse.h>
#include <linux/idr.h>
#include <linux/uio.h>
#define PASSTHROUGH_IOCB_MASK \
(IOCB_APPEND | IOCB_DSYNC | IOCB_HIPRI | IOCB_NOWAIT | IOCB_SYNC)
static void fuse_copyattr(struct file *dst_file, struct file *src_file)
{
struct inode *dst = file_inode(dst_file);
struct inode *src = file_inode(src_file);
i_size_write(dst, i_size_read(src));
}
ssize_t fuse_passthrough_read_iter(struct kiocb *iocb_fuse,
struct iov_iter *iter)
{
ssize_t ret;
struct file *fuse_filp = iocb_fuse->ki_filp;
struct fuse_file *ff = fuse_filp->private_data;
struct file *passthrough_filp = ff->passthrough.filp;
if (!iov_iter_count(iter))
return 0;
ret = vfs_iter_read(passthrough_filp, iter, &iocb_fuse->ki_pos,
iocb_to_rw_flags(iocb_fuse->ki_flags,
PASSTHROUGH_IOCB_MASK));
return ret;
}
ssize_t fuse_passthrough_write_iter(struct kiocb *iocb_fuse,
struct iov_iter *iter)
{
ssize_t ret;
struct file *fuse_filp = iocb_fuse->ki_filp;
struct fuse_file *ff = fuse_filp->private_data;
struct inode *fuse_inode = file_inode(fuse_filp);
struct file *passthrough_filp = ff->passthrough.filp;
if (!iov_iter_count(iter))
return 0;
inode_lock(fuse_inode);
file_start_write(passthrough_filp);
ret = vfs_iter_write(passthrough_filp, iter, &iocb_fuse->ki_pos,
iocb_to_rw_flags(iocb_fuse->ki_flags,
PASSTHROUGH_IOCB_MASK));
file_end_write(passthrough_filp);
if (ret > 0)
fuse_copyattr(fuse_filp, passthrough_filp);
inode_unlock(fuse_inode);
return ret;
}
int fuse_passthrough_open(struct fuse_dev *fud,
struct fuse_passthrough_out *pto)