+++ /dev/null
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->Mount Table</TITLE
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-><H1
-><A
-NAME="FILEIO-MOUNT-TABLE">Chapter 21. Mount Table</H1
-><P
->The mount table records the filesystems that are actually active.
-These can be seen as being analogous to mount points in Unix systems.</P
-><P
->There are two sources of mount table entries. Filesystems (or other
-components) may export static entries to the table using the
-<TT
-CLASS="LITERAL"
->MTAB_ENTRY()</TT
-> macro. Alternatively, new entries may
-be installed at run time using the <TT
-CLASS="FUNCTION"
->mount()</TT
->
-function. Both types of entry may be unmounted with the
-<TT
-CLASS="FUNCTION"
->umount()</TT
-> function.</P
-><P
->A mount table entry has the following structure:</P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
->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
-};</PRE
-></TD
-></TR
-></TABLE
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->name</I
-></TT
-> 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 <TT
-CLASS="STRUCTFIELD"
-><I
->name</I
-></TT
-> 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 <TT
-CLASS="STRUCTFIELD"
-><I
->root</I
-></TT
-> field as the directory
-pointer.</P
-><P
->For example, consider a mount table that contains the following
-entries:</P
-><TABLE
-BORDER="5"
-BGCOLOR="#E0E0F0"
-WIDTH="70%"
-><TR
-><TD
-><PRE
-CLASS="PROGRAMLISTING"
-> { "/", "msdos", "/dev/hd0", ... }
- { "/fd", "msdos", "/dev/fd0", ... }
- { "/rom", "romfs", "", ... }
- { "/tmp", "ramfs", "", ... }
- { "/dev", "devfs", "", ... }</PRE
-></TD
-></TR
-></TABLE
-><P
->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.</P
-><P
->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.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->fsname</I
-></TT
-> field points to a string that
-should match the <TT
-CLASS="STRUCTFIELD"
-><I
->name</I
-></TT
-> field of the
-implementing filesystem. During initialization the mount table is
-scanned and the <TT
-CLASS="STRUCTFIELD"
-><I
->fsname</I
-></TT
-> 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 <TT
-CLASS="STRUCTFIELD"
-><I
->fs</I
-></TT
-> pointer installed.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->devname</I
-></TT
-> 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.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->data</I
-></TT
-> field is a private data value. This
-may be installed either statically when the table entry is defined, or
-may be installed during the <TT
-CLASS="FUNCTION"
->mount()</TT
-> operation.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->valid</I
-></TT
-> field indicates whether this mount
-point has actually been mounted successfully. Entries with a false
-<TT
-CLASS="STRUCTFIELD"
-><I
->valid</I
-></TT
-> field are ignored when searching for a
-name match.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->fs</I
-></TT
-> field is installed after a successful
-<TT
-CLASS="FUNCTION"
->mount()</TT
-> operation to point to the implementing
-filesystem.</P
-><P
->The <TT
-CLASS="STRUCTFIELD"
-><I
->root</I
-></TT
-> field contains a directory pointer
-value that the filesystem can interpret as the root of its directory
-tree. This is passed as the <TT
-CLASS="PARAMETER"
-><I
->dir</I
-></TT
-> argument of
-filesystem functions that operate on rooted filenames. This field must
-be initialized by the filesystem's <TT
-CLASS="FUNCTION"
->mount()</TT
->
-function.</P
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