This series adds two features to erofs for file-backed mounts:

1. Accept a source file descriptor via fsconfig(FSCONFIG_SET_FD,
  "source", NULL, fd) as an alternative to a path string.  This is
  useful when the backing file isn't reachable by path in the caller's
  mount namespace.  For example, composefs reusing an already-mounted
  erofs image's backing file.

2. Add an EROFS_IOC_GET_SOURCE_FD ioctl that returns a file descriptor
  to the backing image file.  This allows userspace to retrieve the
  backing file from an existing erofs mount without needing to know or
  parse the original source path.

Giuseppe Scrivano (2):
  erofs: accept source file descriptor via fsconfig
  erofs: add ioctl to retrieve the backing source file descriptor

 fs/erofs/inode.c           | 25 +++++++++++++++++++++++++
 fs/erofs/super.c           | 36 +++++++++++++++++++++++++-----------
 include/uapi/linux/erofs.h |  9 +++++++++
 3 files changed, 59 insertions(+), 11 deletions(-)
 create mode 100644 include/uapi/linux/erofs.h

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2.55.0