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>Mount Table</TITLE
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>eCos Reference Manual</TH
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><DIV
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CLASS="CHAPTER"
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><H1
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><A
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NAME="FILEIO-MOUNT-TABLE">Chapter 21. Mount Table</H1
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><P
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>The mount table records the filesystems that are actually active.
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These can be seen as being analogous to mount points in Unix systems.</P
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><P
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>There are two sources of mount table entries. Filesystems (or other
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components) may export static entries to the table using the
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<TT
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CLASS="LITERAL"
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>MTAB_ENTRY()</TT
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> macro. Alternatively, new entries may
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be installed at run time using the <TT
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CLASS="FUNCTION"
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>mount()</TT
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>
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function. Both types of entry may be unmounted with the
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<TT
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CLASS="FUNCTION"
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>umount()</TT
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> function.</P
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><P
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>A mount table entry has the following structure:</P
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>struct cyg_mtab_entry
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{
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    const char          *name;          // name of mount point
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    const char          *fsname;        // name of implementing filesystem
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    const char          *devname;       // name of hardware device
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    CYG_ADDRWORD        data;           // private data value
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    cyg_bool            valid;          // Valid entry?
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    cyg_fstab_entry     *fs;            // pointer to fstab entry
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    cyg_dir             root;           // root directory pointer
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};</PRE
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></TD
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></TR
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></TABLE
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><P
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>The <TT
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CLASS="STRUCTFIELD"
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><I
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>name</I
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></TT
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> field identifies the mount
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point. This is used to direct rooted filenames (filenames that
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begin with &quot;/&quot;) to the correct filesystem. When a file
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name that begins with &quot;/&quot; is submitted, it is matched
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against the <TT
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CLASS="STRUCTFIELD"
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><I
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>name</I
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></TT
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> fields of all valid mount
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table entries. The entry that yields the longest match terminating
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before a &quot;/&quot;, or end of string, wins and the appropriate
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function from the filesystem table entry is then passed the remainder
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of the file name together with a pointer to the table entry and the
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value of the <TT
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CLASS="STRUCTFIELD"
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><I
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>root</I
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></TT
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> field as the directory
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pointer.</P
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><P
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>For example, consider a mount table that contains the following
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entries:</P
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><TABLE
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><TR
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><PRE
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CLASS="PROGRAMLISTING"
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>       { "/",    "msdos", "/dev/hd0", ... }
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        { "/fd",  "msdos", "/dev/fd0", ... }
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        { "/rom", "romfs", "", ... }
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        { "/tmp", "ramfs", "", ... }
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        { "/dev", "devfs", "", ... }</PRE
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></TD
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></TR
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></TABLE
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><P
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>An attempt to open &quot;/tmp/foo&quot; would be directed to the RAM
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filesystem while an open of &quot;/bar/bundy&quot; would be directed
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to the hard disc MSDOS filesystem. Opening &quot;/dev/tty0&quot; would
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be directed to the device management filesystem for lookup in the
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device table.</P
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><P
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>Unrooted file names (those that do not begin with a '/') are passed
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straight to the filesystem that contains the current directory. The
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current directory is represented by a pair consisting of a mount table
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entry and a directory pointer.</P
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><P
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>The <TT
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CLASS="STRUCTFIELD"
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><I
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>fsname</I
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></TT
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> field points to a string that
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should match the <TT
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CLASS="STRUCTFIELD"
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><I
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>name</I
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></TT
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> field of the
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implementing filesystem. During initialization the mount table is
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scanned and the <TT
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CLASS="STRUCTFIELD"
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><I
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>fsname</I
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></TT
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> entries looked up in
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the filesystem table. For each match, the filesystem's _mount_
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function is called and if successful the mount table entry is marked
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as valid and the <TT
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CLASS="STRUCTFIELD"
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><I
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>fs</I
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></TT
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> pointer installed.</P
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><P
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>The <TT
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CLASS="STRUCTFIELD"
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><I
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>devname</I
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></TT
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> field contains the name of the
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device that this filesystem is to use. This may match an entry in the
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device table (see later) or may be a string that is specific to the
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filesystem if it has its own internal device drivers.</P
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><P
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>The <TT
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CLASS="STRUCTFIELD"
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><I
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>data</I
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></TT
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> field is a private data value. This
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may be installed either statically when the table entry is defined, or
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may be installed during the <TT
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CLASS="FUNCTION"
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>mount()</TT
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> operation.</P
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><P
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>The <TT
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CLASS="STRUCTFIELD"
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><I
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>valid</I
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></TT
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> field indicates whether this mount
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point has actually been mounted successfully. Entries with a false
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<TT
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CLASS="STRUCTFIELD"
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><I
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>valid</I
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></TT
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> field are ignored when searching for a
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name match.</P
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><P
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>The <TT
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CLASS="STRUCTFIELD"
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><I
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>fs</I
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></TT
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> field is installed after a successful
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<TT
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CLASS="FUNCTION"
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>mount()</TT
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> operation to point to the implementing
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filesystem.</P
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><P
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>The <TT
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CLASS="STRUCTFIELD"
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><I
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>root</I
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></TT
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> field contains a directory pointer
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value that the filesystem can interpret as the root of its directory
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tree. This is passed as the <TT
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CLASS="PARAMETER"
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><I
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>dir</I
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></TT
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> argument of
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filesystem functions that operate on rooted filenames. This field must
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be initialized by the filesystem's <TT
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CLASS="FUNCTION"
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>mount()</TT
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>
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function.</P
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