[PATCH 2/2] erofs: add ioctl to retrieve the backing source file descriptor
From: Giuseppe Scrivano <hidden>
Date: 2026-07-08 09:34:59
Also in:
linux-fsdevel
Subsystem:
erofs file system, filesystems (vfs and infrastructure), the rest · Maintainers:
Gao Xiang, Chao Yu, Alexander Viro, Christian Brauner, Linus Torvalds
Add EROFS_IOC_GET_SOURCE_FD ioctl that returns a file descriptor to the backing image file for file-backed erofs mounts. Returns -ENOENT for block-device-backed erofs mounts where there is no backing file. The UAPI constant is defined in include/uapi/linux/erofs.h. Signed-off-by: Giuseppe Scrivano <redacted> --- fs/erofs/inode.c | 25 +++++++++++++++++++++++++ include/uapi/linux/erofs.h | 9 +++++++++ 2 files changed, 34 insertions(+) create mode 100644 include/uapi/linux/erofs.h
diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index 45afe5c50de8..0a38cb5cfc5d 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c@@ -6,6 +6,8 @@ */ #include "xattr.h" #include <linux/compat.h> +#include <linux/file.h> +#include <uapi/linux/erofs.h> #include <trace/events/erofs.h> static int erofs_fill_symlink(struct inode *inode, void *bptr, unsigned int ofs)
@@ -356,6 +358,27 @@ static int erofs_ioctl_get_volume_label(struct inode *inode, void __user *arg) return ret ? -EFAULT : 0; } +static int erofs_ioctl_get_source_fd(struct file *filp) +{ + struct erofs_sb_info *sbi = EROFS_I_SB(file_inode(filp)); + struct file *f; + int fd; + + if (!capable(CAP_SYS_ADMIN)) + return -EPERM; + + if (!erofs_is_fileio_mode(sbi)) + return -ENOENT; + + fd = get_unused_fd_flags(O_CLOEXEC); + if (fd < 0) + return fd; + + f = get_file(sbi->dif0.file); + fd_install(fd, f); + return fd; +} + long erofs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) { struct inode *inode = file_inode(filp);
@@ -364,6 +387,8 @@ long erofs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) switch (cmd) { case FS_IOC_GETFSLABEL: return erofs_ioctl_get_volume_label(inode, argp); + case EROFS_IOC_GET_SOURCE_FD: + return erofs_ioctl_get_source_fd(filp); default: return -ENOTTY; }
diff --git a/include/uapi/linux/erofs.h b/include/uapi/linux/erofs.h
new file mode 100644
index 000000000000..17c835785ea9
--- /dev/null
+++ b/include/uapi/linux/erofs.h@@ -0,0 +1,9 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _UAPI_LINUX_EROFS_H +#define _UAPI_LINUX_EROFS_H + +#include <linux/ioctl.h> + +#define EROFS_IOC_GET_SOURCE_FD _IO('e', 1) + +#endif /* _UAPI_LINUX_EROFS_H */
--
2.55.0