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