free_mntarg man page on FreeBSD

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KERNEL_MOUNT(9)		 BSD Kernel Developer's Manual	       KERNEL_MOUNT(9)

     free_mntarg, kernel_mount, kernel_vmount, mount_arg, mount_argb,
     mount_argf, mount_argsu — functions provided as part of the kernel mount

     free_mntarg(struct mntarg *ma);

     kernel_mount(struct mntarg *ma, int flags);

     kernel_vmount(int flags, ...);

     struct mntarg *
     mount_arg(struct mntarg *ma, const char *name, const void *val, int len);

     struct mntarg *
     mount_argb(struct mntarg *ma, int flag, const char *name);

     struct mntarg *
     mount_argf(struct mntarg *ma, const char *name, const char *fmt, ...);

     struct mntarg *
     mount_argsu(struct mntarg *ma, const char *name, const void *val,
	 int len);

     The kernel_mount() family of functions are provided as an API for build‐
     ing a list of mount arguments which will be used to mount file systems
     from inside the kernel.  By accumulating a list of arguments, the API
     takes shape and provides the information necessary for the kernel to con‐
     trol the mount(8) utility.	 When an error occurs, the process will stop.
     This will not cause a panic(9).

     The header of the structure is stored in src/sys/kern/vfs_mount.c which
     permits automatic structure creation to ease the mount process.  Memory
     allocation must always be freed when the entire process is complete, it
     is an error otherwise.

     The free_mntarg() function is used to free or clear the mntarg structure.

     The kernel_mount() function pulls information from the structure to per‐
     form the mount request on a given file system.  Additionally, the
     kernel_mount() function always calls the free_mntarg() function.  If ma
     contains any error code generated during the construction, that code will
     be called and the file system mount will not be attempted.

     The kernel_vmount() is a function similar to printf(9) which is used to
     mount a file system.

     The mount_arg() function takes a plain argument and crafts parts of the
     structure with regards to various mount options.  If the length is a
     value less than 0, strlen(3) is used.  This argument will be referenced
     until either free_mntarg() or kernel_mount() is called.

     The mount_argb() function is used to add boolean arguments to the struc‐
     ture.  The flag is the boolean value and name must start with "no", oth‐
     erwise a panic will occur.

     The mount_argf() function adds printf(9) style arguments to the current

     The mount_argsu() function will add arguments to the structure from a
     userland string.

     An example of the *_cmount() function:

     static int
     msdosfs_cmount(struct mntarg *ma, void *data, int flags, struct thread *td)
	     struct msdosfs_args args;
	     int error;

	     if (data == NULL)
		     return (EINVAL);
	     error = copyin(data, &args, sizeof args);
	     if (error)
		     return (error);

	     ma = mount_argsu(ma, "from", args.fspec, MAXPATHLEN);
	     ma = mount_arg(ma, "export", &args.export, sizeof args.export);
	     ma = mount_argf(ma, "uid", "%d", args.uid);
	     ma = mount_argf(ma, "gid", "%d", args.gid);
	     ma = mount_argf(ma, "mask", "%d", args.mask);
	     ma = mount_argf(ma, "dirmask", "%d", args.dirmask);

	     ma = mount_argb(ma, args.flags & MSDOSFSMNT_SHORTNAME, "noshortname");
	     ma = mount_argb(ma, args.flags & MSDOSFSMNT_LONGNAME, "nolongname");
	     ma = mount_argb(ma, !(args.flags & MSDOSFSMNT_NOWIN95), "nowin95");
	     ma = mount_argb(ma, args.flags & MSDOSFSMNT_KICONV, "nokiconv");

	     ma = mount_argsu(ma, "cs_win", args.cs_win, MAXCSLEN);
	     ma = mount_argsu(ma, "cs_dos", args.cs_dos, MAXCSLEN);
	     ma = mount_argsu(ma, "cs_local", args.cs_local, MAXCSLEN);

	     error = kernel_mount(ma, flags);

	     return (error);

     When working with kernel_vmount(), varargs must come in pairs, e.g.,
     {name, value}.

	     error = kernel_vmount(
		 "fstype", vfsname,
		 "fspath", "/",
		 "from", path,

     VFS(9), VFS_MOUNT(9), vfs_mount(9)

     The kernel_mount() family of functions and this manual page first
     appeared in FreeBSD 6.0.

     The kernel_mount() family of functions and API was developed by
     Poul-Henning Kamp ⟨⟩.  This manual page was written by Tom
     Rhodes ⟨⟩.

BSD			       December 13, 2004			   BSD

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