eCos Reference Manual
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# Chapter 21. Mount Table

The mount table records the filesystems that are actually active. These can be seen as being analogous to mount points in Unix systems.

There are two sources of mount table entries. Filesystems (or other components) may export static entries to the table using the `MTAB_ENTRY()` macro. Alternatively, new entries may be installed at run time using the `mount()` function. Both types of entry may be unmounted with the `umount()` function.

A mount table entry has the following structure:

    struct cyg_mtab_entry
    {
        const char          *name;          // name of mount point
        const char          *fsname;        // name of implementing filesystem
        const char          *devname;       // name of hardware device
        CYG_ADDRWORD        data;           // private data value
        cyg_bool            valid;          // Valid entry?
        cyg_fstab_entry     *fs;            // pointer to fstab entry
        cyg_dir             root;           // root directory pointer
    };

The `name` field identifies the mount point. This is used to direct rooted filenames (filenames that begin with "/") to the correct filesystem. When a file name that begins with "/" is submitted, it is matched against the `name` fields of all valid mount table entries. The entry that yields the longest match terminating before a "/", or end of string, wins and the appropriate function from the filesystem table entry is then passed the remainder of the file name together with a pointer to the table entry and the value of the `root` field as the directory pointer.

For example, consider a mount table that contains the following entries:

    	{ "/",    "msdos", "/dev/hd0", ... }
    	{ "/fd",  "msdos", "/dev/fd0", ... }
    	{ "/rom", "romfs", "", ... }
    	{ "/tmp", "ramfs", "", ... }
    	{ "/dev", "devfs", "", ... }

An attempt to open "/tmp/foo" would be directed to the RAM filesystem while an open of "/bar/bundy" would be directed to the hard disc MSDOS filesystem. Opening "/dev/tty0" would be directed to the device management filesystem for lookup in the device table.

Unrooted file names (those that do not begin with a '/') are passed straight to the filesystem that contains the current directory. The current directory is represented by a pair consisting of a mount table entry and a directory pointer.

The `fsname` field points to a string that should match the `name` field of the implementing filesystem. During initialization the mount table is scanned and the `fsname` entries looked up in the filesystem table. For each match, the filesystem's _mount_ function is called and if successful the mount table entry is marked as valid and the `fs` pointer installed.

The `devname` field contains the name of the device that this filesystem is to use. This may match an entry in the device table (see later) or may be a string that is specific to the filesystem if it has its own internal device drivers.

The `data` field is a private data value. This may be installed either statically when the table entry is defined, or may be installed during the `mount()` operation.

The `valid` field indicates whether this mount point has actually been mounted successfully. Entries with a false `valid` field are ignored when searching for a name match.

The `fs` field is installed after a successful `mount()` operation to point to the implementing filesystem.

The `root` field contains a directory pointer value that the filesystem can interpret as the root of its directory tree. This is passed as the `dir` argument of filesystem functions that operate on rooted filenames. This field must be initialized by the filesystem's `mount()` function.

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