Re: [PATCH 11/19] Add support for the new linux mount API

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Mar 24, 2026 at 09:16:03PM +0100, Bernd Schubert wrote:
> 
> 
> On 3/24/26 00:42, Darrick J. Wong wrote:
> > On Mon, Mar 23, 2026 at 06:45:06PM +0100, Bernd Schubert wrote:
> >> From: Bernd Schubert <bschubert@ddn.com>
> >>
> >> So far only supported for fuse_session_mount(), which is called
> >> from high and low level API, but not yet supported for
> >> fuse_open_channel(), which used for privilege drop through
> >> mount.fuse. Main goal for the new API is support for synchronous
> >> FUSE_INIT and I don't think that is going to work with
> >> fuse_open_channel(). At least not with io-uring support as long
> >> as it is started from FUSE_INIT.
> >>
> >> Signed-off-by: Bernd Schubert <bschubert@ddn.com>
> >> ---
> >>  lib/fuse_lowlevel.c |  75 +++++++++-
> >>  lib/meson.build     |   3 +
> >>  lib/mount.c         |  27 +++-
> >>  lib/mount_fsmount.c | 405 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>  lib/mount_i_linux.h |  14 ++
> >>  meson.build         |  19 ++-
> >>  6 files changed, 535 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/lib/fuse_lowlevel.c b/lib/fuse_lowlevel.c
> >> index 4a1c7c4c02a05706e077a7ea89fab3c81bfe22cd..626233df20f49fa89cd9327f94340169d7061f75 100644
> >> --- a/lib/fuse_lowlevel.c
> >> +++ b/lib/fuse_lowlevel.c
> >> @@ -20,6 +20,9 @@
> >>  #include "util.h"
> >>  #include "fuse_uring_i.h"
> >>  #include "fuse_daemonize.h"
> >> +#if defined(__linux__)
> >> +#include "mount_i_linux.h"
> >> +#endif
> >>  
> >>  #include <pthread.h>
> >>  #include <stdatomic.h>
> >> @@ -4398,6 +4401,64 @@ int fuse_session_custom_io_30(struct fuse_session *se,
> >>  			offsetof(struct fuse_custom_io, clone_fd), fd);
> >>  }
> >>  
> >> +#if defined(HAVE_NEW_MOUNT_API)
> >> +/* Only linux supports sync FUSE_INIT so far */
> > 
> > What does synchronous FUSE_INIT have to do with fsmount()?
> > Does it not work with the old mount(2)?
> 
> So we had this discussion with Miklos in the earlier version of the
> patches here https://github.com/libfuse/libfuse/pull/1367
> where Miklos has noticed the possible deadlock and suggested the new 
> mount API. I think Miklos kernel patch solves that, without the new 
> mount API, but then I'm now hesitating to make the code even more
> complex by supported old and new API. Until BSD gains that sync-fuse
> init, this is a Linux only feature and was added after new the new mount
> api. 
> 
> The comment is not right for this commit, though.

Oh ok.  I saw that discussion with Miklos about the deadlock ended in a
patch to just abort the connection if the server crashed during
FUSE_INIT.

I think it's perfectly legit to limit the new sync_init API to fsmount.
:)

> >> +static int fuse_session_mount_new_api(struct fuse_session *se,
> >> +				      const char *mountpoint)
> >> +{
> >> +	int fd = -1;
> >> +	int res, err;
> >> +	char *mnt_opts = NULL;
> >> +	char *mnt_opts_with_fd = NULL;
> >> +	char fd_opt[32];
> >> +
> >> +	res = fuse_kern_mount_get_base_mnt_opts(se->mo, &mnt_opts);
> >> +	if (res == -1) {
> >> +		fuse_log(FUSE_LOG_ERR,
> >> +			 "fuse: failed to get base mount options\n");
> >> +		err = -EIO;
> >> +		goto err;
> >> +	}
> >> +
> >> +	fd = fuse_kern_mount_prepare(mountpoint, se->mo);
> >> +	if (fd == -1) {
> >> +		fuse_log(FUSE_LOG_ERR, "Mount preparation failed.\n");
> >> +		err = -EIO;
> >> +		goto err;
> >> +	}
> >> +
> >> +	snprintf(fd_opt, sizeof(fd_opt), "fd=%i", fd);
> >> +	if (fuse_opt_add_opt(&mnt_opts_with_fd, mnt_opts) == -1 ||
> >> +	    fuse_opt_add_opt(&mnt_opts_with_fd, fd_opt) == -1) {
> >> +		err = -ENOMEM;
> >> +		goto err;
> >> +	}
> >> +
> >> +	err = fuse_kern_fsmount_mo(mountpoint, se->mo, mnt_opts_with_fd);
> >> +err:
> >> +	if (err) {
> >> +		if (fd >= 0)
> >> +			close(fd);
> >> +		fd = -1;
> >> +		se->fd = -1;
> >> +		se->error = -errno;
> >> +	}
> >> +
> >> +	free(mnt_opts);
> >> +	free(mnt_opts_with_fd);
> >> +	return fd;
> >> +}
> >> +#else
> >> +static int fuse_session_mount_new_api(struct fuse_session *se,
> >> +				      const char *mountpoint)
> >> +{
> >> +	(void)se;
> >> +	(void)mountpoint;
> >> +
> >> +	return -1;
> >> +}
> >> +#endif
> >> +
> >>  int fuse_session_mount(struct fuse_session *se, const char *_mountpoint)
> >>  {
> >>  	int fd;
> >> @@ -4425,6 +4486,8 @@ int fuse_session_mount(struct fuse_session *se, const char *_mountpoint)
> >>  			close(fd);
> >>  	} while (fd >= 0 && fd <= 2);
> >>  
> >> +	/* Open channel */
> >> +
> >>  	/*
> >>  	 * To allow FUSE daemons to run without privileges, the caller may open
> >>  	 * /dev/fuse before launching the file system and pass on the file
> >> @@ -4443,10 +4506,18 @@ int fuse_session_mount(struct fuse_session *se, const char *_mountpoint)
> >>  		return 0;
> >>  	}
> >>  
> >> -	/* Open channel */
> >> +	/* new linux mount api */
> >> +	fd = fuse_session_mount_new_api(se, mountpoint);
> >> +	if (fd >= 0)
> >> +		goto out;
> >> +
> >> +	/* fall back to old API */
> >> +	se->error = 0; /* reset error of new api */
> >>  	fd = fuse_kern_mount(mountpoint, se->mo);
> >> -	if (fd == -1)
> >> +	if (fd < 0)
> >>  		goto error_out;
> >> +
> >> +out:
> >>  	se->fd = fd;
> >>  
> >>  	/* Save mountpoint */
> >> diff --git a/lib/meson.build b/lib/meson.build
> >> index 5bd449ebffe7c9229df904d647d990c6c47f80b5..5fd738a589c5aba97a738d5eedbf0f9962e4adfc 100644
> >> --- a/lib/meson.build
> >> +++ b/lib/meson.build
> >> @@ -7,6 +7,9 @@ libfuse_sources = ['fuse.c', 'fuse_i.h', 'fuse_loop.c', 'fuse_loop_mt.c',
> >>  
> >>  if host_machine.system().startswith('linux')
> >>     libfuse_sources += [ 'mount.c' ]
> >> +   if private_cfg.get('HAVE_NEW_MOUNT_API', false)
> >> +      libfuse_sources += [ 'mount_fsmount.c' ]
> >> +   endif
> >>  else
> >>     libfuse_sources += [ 'mount_bsd.c' ]
> >>  endif
> >> diff --git a/lib/mount.c b/lib/mount.c
> >> index b3ee9ba4c0a74c1d0d55f916e7046e064f8468b0..30fd4d2f9bbb84c817b2363b2075456acd1c1255 100644
> >> --- a/lib/mount.c
> >> +++ b/lib/mount.c
> >> @@ -449,8 +449,8 @@ static int fuse_mount_fusermount(const char *mountpoint, struct mount_opts *mo,
> >>  #define O_CLOEXEC 0
> >>  #endif
> >>  
> >> -static int fuse_kern_mount_prepare(const char *mnt,
> >> -				   struct mount_opts *mo)
> >> +int fuse_kern_mount_prepare(const char *mnt,
> >> +			    struct mount_opts *mo)
> >>  {
> >>  	char tmp[128];
> >>  	const char *devname = fuse_mnt_get_devname();
> >> @@ -500,6 +500,26 @@ out_close:
> >>  	return -1;
> >>  }
> >>  
> >> +#if defined(HAVE_NEW_MOUNT_API)
> >> +/**
> >> + * Wrapper for fuse_kern_fsmount that accepts struct mount_opts
> >> + * @mnt: mountpoint
> >> + * @mo: mount options
> >> + * @mnt_opts: mount options to pass to the kernel
> >> + *
> >> + * Returns: 0 on success, -1 on failure with errno set
> >> + */
> >> +int fuse_kern_fsmount_mo(const char *mnt, struct mount_opts *mo,
> >> +			 const char *mnt_opts)
> >> +{
> >> +	const char *devname = fuse_mnt_get_devname();
> >> +
> >> +	return fuse_kern_fsmount(mnt, mo->flags, mo->blkdev, mo->fsname,
> >> +				 mo->subtype, devname, mo->kernel_opts,
> >> +				 mnt_opts);
> >> +}
> >> +#endif
> >> +
> >>  /**
> >>   * Complete the mount operation with an already-opened fd
> >>   * @mnt: mountpoint
> >> @@ -643,8 +663,7 @@ void destroy_mount_opts(struct mount_opts *mo)
> >>  	free(mo);
> >>  }
> >>  
> >> -static int fuse_kern_mount_get_base_mnt_opts(struct mount_opts *mo,
> >> -					     char **mnt_optsp)
> >> +int fuse_kern_mount_get_base_mnt_opts(struct mount_opts *mo, char **mnt_optsp)
> >>  {
> >>  	if (get_mnt_flag_opts(mnt_optsp, mo->flags) == -1)
> >>  		return -1;
> >> diff --git a/lib/mount_fsmount.c b/lib/mount_fsmount.c
> >> new file mode 100644
> >> index 0000000000000000000000000000000000000000..cba998bc60c783a5edc0c16570f7e5512b7f1253
> >> --- /dev/null
> >> +++ b/lib/mount_fsmount.c
> >> @@ -0,0 +1,405 @@
> >> +/*
> >> + *  FUSE: Filesystem in Userspace
> >> + *  Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>
> >> + *                2026 Bernd Schubert <bernd@bsbernd.com>
> >> + *
> >> + * New Linux mount API (fsopen/fsconfig/fsmount/move_mount) support.
> >> + *
> >> + *  This program can be distributed under the terms of the GNU LGPLv2.
> >> + *  See the file LGPL2.txt.
> >> + */
> >> +
> >> +#define _GNU_SOURCE
> >> +
> >> +#include "fuse_config.h"
> >> +#include "fuse_misc.h"
> >> +#include "mount_util.h"
> >> +#include "mount_i_linux.h"
> >> +
> >> +#include <stdio.h>
> >> +#include <stdlib.h>
> >> +#include <unistd.h>
> >> +#include <string.h>
> >> +#include <fcntl.h>
> >> +#include <errno.h>
> >> +#include <sys/mount.h>
> >> +#include <sys/syscall.h>
> >> +
> >> +/* Mount attribute flags for fsmount() - from linux/mount.h */
> >> +#ifndef MOUNT_ATTR_RDONLY
> >> +#define MOUNT_ATTR_RDONLY       0x00000001
> >> +#endif
> >> +#ifndef MOUNT_ATTR_NOSUID
> >> +#define MOUNT_ATTR_NOSUID       0x00000002
> >> +#endif
> >> +#ifndef MOUNT_ATTR_NODEV
> >> +#define MOUNT_ATTR_NODEV        0x00000004
> >> +#endif
> >> +#ifndef MOUNT_ATTR_NOEXEC
> >> +#define MOUNT_ATTR_NOEXEC       0x00000008
> >> +#endif
> >> +#ifndef MOUNT_ATTR__ATIME
> >> +#define MOUNT_ATTR__ATIME       0x00000070
> >> +#endif
> >> +#ifndef MOUNT_ATTR_RELATIME
> >> +#define MOUNT_ATTR_RELATIME     0x00000000
> >> +#endif
> >> +#ifndef MOUNT_ATTR_NOATIME
> >> +#define MOUNT_ATTR_NOATIME      0x00000010
> >> +#endif
> >> +#ifndef MOUNT_ATTR_STRICTATIME
> >> +#define MOUNT_ATTR_STRICTATIME  0x00000020
> >> +#endif
> >> +#ifndef MOUNT_ATTR_NODIRATIME
> >> +#define MOUNT_ATTR_NODIRATIME   0x00000080
> >> +#endif
> >> +#ifndef MOUNT_ATTR_NOSYMFOLLOW
> >> +#define MOUNT_ATTR_NOSYMFOLLOW  0x00200000
> >> +#endif
> > 
> > /me notes that all MOUNT_ATTR_ before NOSYMFOLLOW were introduced in the
> > initial commit so if the meson test thinks the new fsmount api is
> > present then you can rely on flags being defined.
> 
> Thanks, removed those flags and added a comment.
> 
> > 
> >> +
> >> +/*
> >> + * Convert MS_* mount flags to MOUNT_ATTR_* mount attributes.
> >> + * These flags are passed to fsmount(), not fsconfig().
> >> + * Mount attributes control mount-point level behavior.
> >> + */
> >> +static unsigned long ms_flags_to_mount_attrs(unsigned long flags)
> >> +{
> >> +	unsigned long attrs = 0;
> >> +
> >> +	if (flags & MS_NOSUID)
> >> +		attrs |= MOUNT_ATTR_NOSUID;
> >> +	if (flags & MS_NODEV)
> >> +		attrs |= MOUNT_ATTR_NODEV;
> >> +	if (flags & MS_NOEXEC)
> >> +		attrs |= MOUNT_ATTR_NOEXEC;
> >> +	if (flags & MS_NOATIME)
> >> +		attrs |= MOUNT_ATTR_NOATIME;
> >> +	else if (flags & MS_RELATIME)
> >> +		attrs |= MOUNT_ATTR_RELATIME;
> >> +	else if (flags & MS_STRICTATIME)
> >> +		attrs |= MOUNT_ATTR_STRICTATIME;
> >> +	if (flags & MS_NODIRATIME)
> >> +		attrs |= MOUNT_ATTR_NODIRATIME;
> >> +	if (flags & MS_NOSYMFOLLOW)
> >> +		attrs |= MOUNT_ATTR_NOSYMFOLLOW;
> >> +
> >> +	return attrs;
> >> +}
> >> +
> >> +/*
> >> + * Apply VFS superblock flags to the filesystem context.
> >> + * Only handles flags that are filesystem parameters (ro, sync, dirsync).
> >> + * Mount attributes (nosuid, nodev, etc.) are handled separately via fsmount().
> >> + */
> >> +static int apply_mount_flags(int fsfd, unsigned long flags)
> >> +{
> >> +	int res;
> >> +
> >> +	/* Handle read-only flag */
> >> +	if (flags & MS_RDONLY) {
> >> +		res = fsconfig(fsfd, FSCONFIG_SET_FLAG, "ro", NULL, 0);
> >> +		if (res == -1) {
> >> +			fprintf(stderr,
> >> +				"fuse: fsconfig SET_FLAG ro failed: %s\n",
> >> +				strerror(errno));
> >> +			return -errno;
> >> +		}
> >> +	}
> >> +
> >> +	/* Handle sync flag */
> >> +	if (flags & MS_SYNCHRONOUS) {
> >> +		res = fsconfig(fsfd, FSCONFIG_SET_FLAG, "sync", NULL, 0);
> >> +		if (res == -1) {
> >> +			fprintf(stderr,
> >> +				"fuse: fsconfig SET_FLAG sync failed: %s\n",
> >> +				strerror(errno));
> >> +			return -errno;
> >> +		}
> >> +	}
> >> +
> >> +#ifndef __NetBSD__
> >> +	/* Handle dirsync flag */
> >> +	if (flags & MS_DIRSYNC) {
> >> +		res = fsconfig(fsfd, FSCONFIG_SET_FLAG, "dirsync", NULL, 0);
> >> +		if (res == -1) {
> >> +			fprintf(stderr,
> >> +				"fuse: fsconfig SET_FLAG dirsync failed: %s\n",
> >> +				strerror(errno));
> >> +			return -errno;
> >> +		}
> >> +	}
> >> +#endif
> >> +
> >> +	return 0;
> >> +}
> > 
> > Oh, nice treatment of the MS_ flags that don't have a corresponding
> > MOUNT_ATTR_ flag.  I should incorporate that into mount_service.c.
> > 
> >> +
> >> +static int apply_opt_fd(int fsfd, const char *value)
> >> +{
> >> +	int res;
> >> +
> >> +	/* The fd parameter is a u32 value, not a file descriptor to pass */
> >> +	res = fsconfig(fsfd, FSCONFIG_SET_STRING, "fd", value, 0);
> >> +	if (res == -1) {
> >> +		fprintf(stderr, "fuse: fsconfig SET_STRING fd=%s failed: %s\n",
> >> +			value, strerror(errno));
> >> +		return -errno;
> > 
> > Did you know that you can read the kernel's error messages from the
> > fsopen fd?
> > 
> > https://git.kernel.org/pub/scm/linux/kernel/git/djwong/libfuse.git/tree/util/mount_service.c?h=fuse-service-container&id=d02bbab680ab4689bbd5e274735e91bd38e5f47f#n693
> 
> Ah nice, I kind of copied over this function now.

:)

> > 
> >> +	}
> >> +	return 0;
> >> +}
> >> +
> >> +static int apply_opt_string(int fsfd, const char *key, const char *value)
> >> +{
> >> +	int res;
> >> +
> >> +	res = fsconfig(fsfd, FSCONFIG_SET_STRING, key, value, 0);
> >> +	if (res == -1) {
> >> +		fprintf(stderr,
> >> +			"fuse: fsconfig SET_STRING %s=%s failed: %s\n",
> >> +			key, value, strerror(errno));
> >> +		return -errno;
> > 
> > I think you have to save errno explicitly here, because fprintf and
> > strerror could fail and set errno to something else.  For example, if
> > fsconfig returns EINVAL but stderr points to a file on a completely full
> > filesystem, the ENOSPC from the fprintf call (or more likely the write()
> > underneath it) will obliterate the EINVAL.
> 
> Absolutely, had slipped through. Thank you!

(I hate C error handling so much...)

> > 
> >> +	}
> >> +	return 0;
> >> +}
> >> +
> >> +static int apply_opt_flag(int fsfd, const char *opt)
> >> +{
> >> +	int res;
> >> +
> >> +	res = fsconfig(fsfd, FSCONFIG_SET_FLAG, opt, NULL, 0);
> >> +	if (res == -1) {
> >> +		fprintf(stderr, "fuse: fsconfig SET_FLAG %s failed: %s\n",
> >> +			opt, strerror(errno));
> >> +		return -errno;
> >> +	}
> >> +	return 0;
> >> +}
> >> +
> >> +static int apply_opt_key_value(int fsfd, char *opt)
> >> +{
> >> +	char *eq;
> >> +	const char *key;
> >> +	const char *value;
> >> +
> >> +	eq = strchr(opt, '=');
> >> +	if (!eq)
> >> +		return apply_opt_flag(fsfd, opt);
> >> +
> >> +	*eq = '\0';
> >> +	key = opt;
> >> +	value = eq + 1;
> >> +
> >> +	if (strcmp(key, "fd") == 0)
> >> +		return apply_opt_fd(fsfd, value);
> >> +
> >> +	return apply_opt_string(fsfd, key, value);
> >> +}
> >> +
> >> +/**
> >> + * Check if an option is a mount attribute (handled by fsmount, not fsconfig)
> >> + */
> >> +static int is_mount_attr_opt(const char *opt)
> >> +{
> >> +	/* These options are mount attributes passed to fsmount(), not fsconfig() */
> >> +	return strcmp(opt, "nosuid") == 0 ||
> >> +	       strcmp(opt, "suid") == 0 ||
> >> +	       strcmp(opt, "nodev") == 0 ||
> >> +	       strcmp(opt, "dev") == 0 ||
> >> +	       strcmp(opt, "noexec") == 0 ||
> >> +	       strcmp(opt, "exec") == 0 ||
> >> +	       strcmp(opt, "noatime") == 0 ||
> >> +	       strcmp(opt, "atime") == 0 ||
> >> +	       strcmp(opt, "nodiratime") == 0 ||
> >> +	       strcmp(opt, "diratime") == 0 ||
> >> +	       strcmp(opt, "relatime") == 0 ||
> >> +	       strcmp(opt, "norelatime") == 0 ||
> >> +	       strcmp(opt, "strictatime") == 0 ||
> >> +	       strcmp(opt, "nostrictatime") == 0 ||
> >> +	       strcmp(opt, "nosymfollow") == 0 ||
> >> +	       strcmp(opt, "symfollow") == 0;
> >> +}
> >> +
> >> +/*
> >> + * Parse kernel options string and apply via fsconfig
> >> + * Options are comma-separated key=value pairs
> >> + */
> >> +static int apply_mount_opts(int fsfd, const char *opts)
> >> +{
> >> +	char *opts_copy;
> >> +	char *opt;
> >> +	char *saveptr;
> >> +	int res;
> >> +
> >> +	if (!opts || !*opts)
> >> +		return 0;
> >> +
> >> +	opts_copy = strdup(opts);
> >> +	if (!opts_copy) {
> >> +		fprintf(stderr, "fuse: failed to allocate memory\n");
> >> +		return -ENOMEM;
> >> +	}
> >> +
> >> +	opt = strtok_r(opts_copy, ",", &saveptr);
> >> +	while (opt) {
> >> +		/* Skip mount attributes - they're handled by fsmount(), not fsconfig() */
> >> +		if (!is_mount_attr_opt(opt)) {
> >> +			res = apply_opt_key_value(fsfd, opt);
> > 
> > Does fuse_session_new_versioned convert those magic string flags from
> > is_mount_attr_opt into their MS_* equivalents such that apply_mount_opts
> > won't see the string versions?
> 
> Comment updated to
> 
> 		/*
> 		 * Skip mount attributes, they're handled by fsmount()
> 		 * not fsconfig().
> 		 *
> 		 * These string options (nosuid, nodev, etc.) are reconstructed
> 		 * from MS_* flags by get_mnt_flag_opts() in lib/mount.c and
> 		 * get_mnt_opts() in util/fusermount.c. Both the library path
> 		 * (via fuse_kern_mount_get_base_mnt_opts) and fusermount3 path
> 		 * rebuild these strings from the flags bitmask and pass them in
> 		 * mnt_opts. They must be filtered here because they are mount
> 		 * attributes (passed to fsmount via MOUNT_ATTR_*), not
> 		 * filesystem parameters (which would be passed to fsconfig).
> 		 */
> 		if (!is_mount_attr_opt(opt)) {

That clears things right up, thanks!

> 
> > 
> >> +			if (res < 0) {
> >> +				free(opts_copy);
> >> +				return res;
> >> +			}
> >> +		}
> >> +		opt = strtok_r(NULL, ",", &saveptr);
> >> +	}
> >> +
> >> +	free(opts_copy);
> >> +	return 0;
> >> +}
> >> +
> >> +
> >> +/**
> >> + * Mount using the new Linux mount API (fsopen/fsconfig/fsmount/move_mount)
> >> + * @mnt: mountpoint
> >> + * @flags: mount flags (MS_NOSUID, MS_NODEV, etc.)
> >> + * @blkdev: 1 for fuseblk, 0 for fuse
> >> + * @fsname: filesystem name (or NULL)
> >> + * @subtype: filesystem subtype (or NULL)
> >> + * @source_dev: device name for building source string
> >> + * @kernel_opts: kernel mount options string
> >> + * @mnt_opts: additional mount options to pass to the kernel
> >> + *
> >> + * Returns: 0 on success, -1 on failure with errno set
> >> + */
> >> +int fuse_kern_fsmount(const char *mnt, unsigned long flags, int blkdev,
> >> +		      const char *fsname, const char *subtype,
> >> +		      const char *source_dev, const char *kernel_opts,
> >> +		      const char *mnt_opts)
> >> +{
> >> +	const char *type;
> >> +	char *source = NULL;
> >> +	int fsfd = -1;
> >> +	int mntfd = -1;
> >> +	int err, res;
> >> +	unsigned long mount_attrs;
> >> +
> >> +	/* Determine filesystem type */
> >> +	type = blkdev ? "fuseblk" : "fuse";
> >> +
> >> +	/* Try to open filesystem context */
> >> +	fsfd = fsopen(type, FSOPEN_CLOEXEC);
> >> +	if (fsfd == -1) {
> >> +		fprintf(stderr, "fuse: fsopen(%s) failed: %s\n", type,
> >> +			strerror(errno));
> >> +		return -1;
> >> +	}
> >> +
> >> +	/* Build source string */
> >> +	source = malloc((fsname ? strlen(fsname) : 0) +
> >> +			(subtype ? strlen(subtype) : 0) +
> >> +			strlen(source_dev) + 32);
> >> +	err = -ENOMEM;
> >> +	if (!source) {
> >> +		fprintf(stderr, "fuse: failed to allocate memory\n");
> >> +		goto out_close_fsfd;
> >> +	}
> >> +
> >> +	strcpy(source, fsname ? fsname : (subtype ? subtype : source_dev));
> > 
> > This is almost fuse_mnt_build_source()
> 
> Yeah, we don't have struct mount_opts that fuse_mnt_build_source() takes.
> Going to improve that in a later patch.

<nod> I reworked my patchset to pull in some of your hoisted helpers so
that rebasing my patchset won't be quite so annoying later.  Will look
forward to whatever form that takes.

--D

> 
> Thanks,
> Bernd
>