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 <[email protected]> --- 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
