Re: [PATCH 0/7] fix up issues from djwong/fuse4fs-fork

Darrick J. Wong
2026-05-06T16:39:36Z

On Wed, May 06, 2026 at 05:08:33PM +0200, Theodore Tso wrote:
> On Wed, May 06, 2026 at 07:34:13AM -0700, Darrick J. Wong wrote:
> > [cc fuse-devel]
> >
> > TLDR for the fuse developers: Ted and I discovered a collision between
> > the upstream libfuse feature bits and the MacFUSE feature bits, which
> > causes macfuse to do the wrong thing if you try to enable symlink
> > pagecache.
>
> This is the patch for fuse2fs and fuse4fs in e2fsprogs which works
> around the problem (tested on MacOS using macfuse 5.2.0_1 from
> MacPorts). More details about why it was needed is in the commit
> description.
>
> - Ted
>
> From 67f1ec55a1309abead16cad883e38b798a567191 Mon Sep 17 00:00:00 2001
> From: Theodore Ts'o <tytso@mit.edu>
> Date: Wed, 6 May 2026 10:51:56 -0400
> Subject: [PATCH] fuse2fs, fuse4fs: Fix MacFuse compatibility issue
>
> Unfortunately, MacFuse is overloading the top bits of the flags field
> in struct fuse_init_{out} for MacFuse-specific capability extensions.
> This results in an attempt to use FUSE_CAP_CACHE_SYMLINKS when linking
> with the libfuse in MacPorts will end up enabling
> FUSE_DARWIN_CAP_ACCESS_EXT with MacFuse. Hilarity then ensues with
> all non-privileged access failing with permission denied.
>
> The change which is needed in MacFuse is described in a TODO(bf)
> statement:
>
> https://github.com/macfuse/library/blob/ddb630db8327a50b6670ef5e4f5e6da82a549e99/lib/fuse_lowlevel.c#L3415
>
> I plan to submit a bug report to MacFuse, but in the mean time, work around
> the problem by disabling the overloaded capability flags on MacOS.
>
> Link: https://lore.kernel.org/r/20260505225635.GT7765@frogsfrogsfrogs
> Link: https://lore.kernel.org/r/20260506092858.GC49070@macsyma.local
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Looks fine for now...
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
> fuse4fs/fuse4fs.c | 18 ++++++++++++++++++
> misc/fuse2fs.c | 18 ++++++++++++++++++
> 2 files changed, 36 insertions(+)
>
> diff --git a/fuse4fs/fuse4fs.c b/fuse4fs/fuse4fs.c
> index 92847326..2739da92 100644
> --- a/fuse4fs/fuse4fs.c
> +++ b/fuse4fs/fuse4fs.c
> @@ -120,6 +120,24 @@
> #endif
> #endif /* !defined(ENODATA) */
>
> +#ifdef __APPLE__
> +/*
> + * Sigh.... MacFuse is overloading the top bits of the flags field in
> + * struct fuse_init_{out} for MacFuse-specific capability extensions.
> + * Avoid using these fuse3 capability flags until this gets fixed in
> + * MacFUSE
> + */
> +#undef FUSE_CAP_CACHE_SYMLINKS
> +#undef FUSE_CAP_NO_OPENDIR_SUPPORT
> +#undef FUSE_CAP_EXPLICIT_INVAL_DATA
> +#undef FUSE_CAP_EXPIRE_ONLY
> +#undef FUSE_CAP_SETXATTR_EXT
> +#undef FUSE_CAP_DIRECT_IO_ALLOW_MMAP
> +#undef FUSE_CAP_PASSTHROUGH
> +#undef FUSE_CAP_NO_EXPORT_SUPPORT
> +#undef FUSE_CAP_OVER_IO_URING
> +#endif
> +
> #define FUSE4FS_ATTR_TIMEOUT (0.0)
>
> static inline uint64_t round_up(uint64_t b, unsigned int align)
> diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
> index c46cfc23..0f2a3c35 100644
> --- a/misc/fuse2fs.c
> +++ b/misc/fuse2fs.c
> @@ -116,6 +116,24 @@
> #endif
> #endif /* !defined(ENODATA) */
>
> +#ifdef __APPLE__
> +/*
> + * Sigh.... MacFuse is overloading the top bits of the flags field in
> + * struct fuse_init_{out} for MacFuse-specific capability extensions.
> + * Avoid using these fuse3 capability flags until this gets fixed in
> + * MacFUSE
> + */
> +#undef FUSE_CAP_CACHE_SYMLINKS
> +#undef FUSE_CAP_NO_OPENDIR_SUPPORT
> +#undef FUSE_CAP_EXPLICIT_INVAL_DATA
> +#undef FUSE_CAP_EXPIRE_ONLY
> +#undef FUSE_CAP_SETXATTR_EXT
> +#undef FUSE_CAP_DIRECT_IO_ALLOW_MMAP
> +#undef FUSE_CAP_PASSTHROUGH
> +#undef FUSE_CAP_NO_EXPORT_SUPPORT
> +#undef FUSE_CAP_OVER_IO_URING
> +#endif
> +
> static inline uint64_t round_up(uint64_t b, unsigned int align)
> {
> unsigned int m;
> --
> 2.50.1 (Apple Git-155)
>