Comtrol eCos - Manual (Page 419)

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.
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