kernel_vmount(9) functions provided as part of the kernel mount interface

Other Alias

free_mntarg, kernel_mount, mount_arg, mount_argb, mount_argf, mount_argsu


Ft void Fn free_mntarg struct mntarg *ma Ft int Fn kernel_mount struct mntarg *ma int flags Ft int Fn kernel_vmount int flags ... Ft struct mntarg * Fo mount_arg Fa struct mntarg *ma const char *name const void *val int len Fc Ft struct mntarg * Fn mount_argb struct mntarg *ma int flag const char *name Ft struct mntarg * Fn mount_argf struct mntarg *ma const char *name const char *fmt ... Ft struct mntarg * Fo mount_argsu Fa struct mntarg *ma const char *name const void *val int len Fc


The Fn kernel_mount family of functions are provided as an API for building 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 control 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 Fn free_mntarg function is used to free or clear the Vt mntarg structure.

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

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

The Fn 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 Fn free_mntarg or Fn kernel_mount is called.

The Fn mount_argb function is used to add boolean arguments to the structure. The Fa flag is the boolean value and Fa name must start with Qq Li no , otherwise a panic will occur.

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

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


An example of the Fn *_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 Fn kernel_vmount , Fa varargs must come in pairs, e.g., Br q Va name , value .

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


The Fn kernel_mount family of functions and this manual page first appeared in Fx 6.0 .


An -nosplit The Fn kernel_mount family of functions and API was developed by An Poul-Henning Kamp Aq [email protected] . This manual page was written by An Tom Rhodes Aq [email protected] .