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<!-- Copyright (C) 2003 Red Hat, Inc.                                --><!-- This material may be distributed only subject to the terms      --><!-- and conditions set forth in the Open Publication License, v1.0  --><!-- or later (the latest version is presently available at          --><!-- http://www.opencontent.org/openpub/).                           --><!-- Distribution of the work or derivative of the work in any       --><!-- standard (paper) book form is prohibited unless prior           --><!-- permission is obtained from the copyright holder.               --><HTML><HEAD><TITLE>Writing a New Filesystem</TITLE><meta name="MSSmartTagsPreventParsing" content="TRUE"><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+"><LINKREL="HOME"TITLE="eCos Reference Manual"HREF="ecos-ref.html"><LINKREL="UP"TITLE="File System Support Infrastructure"HREF="fileio.html"><LINKREL="PREVIOUS"TITLE="Devices"HREF="fileio-devices.html"><LINKREL="NEXT"TITLE="PCI Library"HREF="io-pci.html"></HEAD><BODYCLASS="CHAPTER"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#0000FF"VLINK="#840084"ALINK="#0000FF"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">eCos Reference Manual</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="fileio-devices.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom"></TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="io-pci.html"ACCESSKEY="N">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="CHAPTER"><H1><ANAME="FILEIO-WRITING">Chapter 29. Writing a New Filesystem</H1><P>To create a new filesystem it is necessary to define the fstab entryand the file IO operations. The easiest way to do this is to copy anexisting filesystem: either the test filesystem in the FILEIO package,or the RAM or ROM filesystem packages.</P><P>To make this clearer, the following is a brief tour of the FILEIOrelevant parts of the RAM filesystem.</P><P>First, it is necessary to provide forward definitions of the functionsthat constitute the filesystem interface:</P><TABLEBORDER="5"BGCOLOR="#E0E0F0"WIDTH="70%"><TR><TD><PRECLASS="PROGRAMLISTING">//==========================================================================// Forward definitions// Filesystem operationsstatic int ramfs_mount    ( cyg_fstab_entry *fste, cyg_mtab_entry *mte );static int ramfs_umount   ( cyg_mtab_entry *mte );static int ramfs_open     ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,                             int mode,  cyg_file *fte );static int ramfs_unlink   ( cyg_mtab_entry *mte, cyg_dir dir, const char *name );static int ramfs_mkdir    ( cyg_mtab_entry *mte, cyg_dir dir, const char *name );static int ramfs_rmdir    ( cyg_mtab_entry *mte, cyg_dir dir, const char *name );static int ramfs_rename   ( cyg_mtab_entry *mte, cyg_dir dir1, const char *name1,                             cyg_dir dir2, const char *name2 );static int ramfs_link     ( cyg_mtab_entry *mte, cyg_dir dir1, const char *name1,                             cyg_dir dir2, const char *name2, int type );static int ramfs_opendir  ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,                             cyg_file *fte );static int ramfs_chdir    ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,                             cyg_dir *dir_out );static int ramfs_stat     ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,                             struct stat *buf);static int ramfs_getinfo  ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,                             int key, void *buf, int len );static int ramfs_setinfo  ( cyg_mtab_entry *mte, cyg_dir dir, const char *name,                             int key, void *buf, int len );// File operationsstatic int ramfs_fo_read      (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);static int ramfs_fo_write     (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);static int ramfs_fo_lseek     (struct CYG_FILE_TAG *fp, off_t *pos, int whence );static int ramfs_fo_ioctl     (struct CYG_FILE_TAG *fp, CYG_ADDRWORD com,                                CYG_ADDRWORD data);static int ramfs_fo_fsync     (struct CYG_FILE_TAG *fp, int mode );        static int ramfs_fo_close     (struct CYG_FILE_TAG *fp);static int ramfs_fo_fstat     (struct CYG_FILE_TAG *fp, struct stat *buf );static int ramfs_fo_getinfo   (struct CYG_FILE_TAG *fp, int key, void *buf, int len );static int ramfs_fo_setinfo   (struct CYG_FILE_TAG *fp, int key, void *buf, int len );// Directory operationsstatic int ramfs_fo_dirread      (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);static int ramfs_fo_dirlseek     (struct CYG_FILE_TAG *fp, off_t *pos, int whence );</PRE></TD></TR></TABLE><P>We define all of the fstab entries and all of the file IOoperations. We also define alternatives for the<TTCLASS="STRUCTFIELD"><I>fo_read</I></TT> and<TTCLASS="STRUCTFIELD"><I>fo_lseek</I></TT> file IO operations.</P><P>We can now define the filesystem table entry. There is a macro,<TTCLASS="LITERAL">FSTAB_ENTRY</TT> to do this:</P><TABLEBORDER="5"BGCOLOR="#E0E0F0"WIDTH="70%"><TR><TD><PRECLASS="PROGRAMLISTING">//==========================================================================// Filesystem table entries// -------------------------------------------------------------------------// Fstab entry.// This defines the entry in the filesystem table.// For simplicity we use _FILESYSTEM synchronization for all accesses since// we should never block in any filesystem operations.FSTAB_ENTRY( ramfs_fste, "ramfs", 0,             CYG_SYNCMODE_FILE_FILESYSTEM|CYG_SYNCMODE_IO_FILESYSTEM,             ramfs_mount,             ramfs_umount,             ramfs_open,             ramfs_unlink,             ramfs_mkdir,             ramfs_rmdir,             ramfs_rename,             ramfs_link,             ramfs_opendir,             ramfs_chdir,             ramfs_stat,             ramfs_getinfo,             ramfs_setinfo);</PRE></TD></TR></TABLE><P>The first argument to this macro gives the fstab entry a name, theremainder are initializers for the field of the structure.</P><P>We must also define the file operations table that is installed in allopen file table entries:</P><TABLEBORDER="5"BGCOLOR="#E0E0F0"WIDTH="70%"><TR><TD><PRECLASS="PROGRAMLISTING">// -------------------------------------------------------------------------// File operations.// This set of file operations are used for normal open files.static cyg_fileops ramfs_fileops ={    ramfs_fo_read,    ramfs_fo_write,    ramfs_fo_lseek,    ramfs_fo_ioctl,    cyg_fileio_seltrue,    ramfs_fo_fsync,    ramfs_fo_close,    ramfs_fo_fstat,    ramfs_fo_getinfo,    ramfs_fo_setinfo};</PRE></TD></TR></TABLE><P>These all point to functions supplied by the filesystem except the<TTCLASS="STRUCTFIELD"><I>fo_select</I></TT> field which is filled with apointer to <TTCLASS="FUNCTION">cyg_fileio_seltrue()</TT>. This is providedby the FILEIO package and is a select function that always returnstrue to all operations.</P><P>Finally, we need to define a set of file operations for use whenreading directories. This table only defines the<TTCLASS="STRUCTFIELD"><I>fo_read</I></TT> and<TTCLASS="STRUCTFIELD"><I>fo_lseek</I></TT> operations. The rest are filledwith stub functions supplied by the FILEIO package that just return anerror code.</P><TABLEBORDER="5"BGCOLOR="#E0E0F0"WIDTH="70%"><TR><TD><PRECLASS="PROGRAMLISTING">// -------------------------------------------------------------------------// Directory file operations.// This set of operations are used for open directories. Most entries// point to error-returning stub functions. Only the read, lseek and// close entries are functional.static cyg_fileops ramfs_dirops ={    ramfs_fo_dirread,    (cyg_fileop_write *)cyg_fileio_enosys,    ramfs_fo_dirlseek,    (cyg_fileop_ioctl *)cyg_fileio_enosys,    cyg_fileio_seltrue,    (cyg_fileop_fsync *)cyg_fileio_enosys,    ramfs_fo_close,    (cyg_fileop_fstat *)cyg_fileio_enosys,    (cyg_fileop_getinfo *)cyg_fileio_enosys,    (cyg_fileop_setinfo *)cyg_fileio_enosys};</PRE></TD></TR></TABLE><P>If the filesystem wants to have an instance automatically mounted onsystem startup, it must also define a mount table entry. This is donewith the <TTCLASS="LITERAL">MTAB_ENTRY</TT> macro. This is an example fromthe test filesystem of how this is used:</P><TABLEBORDER="5"BGCOLOR="#E0E0F0"WIDTH="70%"><TR><TD><PRECLASS="PROGRAMLISTING">MTAB_ENTRY( testfs_mte1,                   "/",                   "testfs",                   "",                   0);</PRE></TD></TR></TABLE><P>The first argument provides a name for the table entry. The followingarguments provide initialization for the<TTCLASS="STRUCTFIELD"><I>name</I></TT>, <TTCLASS="STRUCTFIELD"><I>fsname</I></TT>,<TTCLASS="STRUCTFIELD"><I>devname</I></TT> and <TTCLASS="STRUCTFIELD"><I>data</I></TT>fields respectively.</P><P>These definitions are adequate to let the new filesystem interactwith the FILEIO package. The new filesystem now needs to be fleshedout with implementations of the functions defined above. Obviously,the exact form this takes will depend on what the filesystem isintended to do. Take a look at the RAM and ROM filesystems forexamples of how this has been done.</P></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLESUMMARY="Footer navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="fileio-devices.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="ecos-ref.html"ACCESSKEY="H">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="io-pci.html"ACCESSKEY="N">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">Devices</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="fileio.html"ACCESSKEY="U">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">PCI Library</TD></TR></TABLE></DIV></BODY></HTML>
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