--- /dev/null
+<!-- Copyright (C) 2003 Red Hat, Inc. -->
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+<HTML
+><HEAD
+><TITLE
+>File Table</TITLE
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+TITLE="eCos Reference Manual"
+HREF="ecos-ref.html"><LINK
+REL="UP"
+TITLE="File System Support Infrastructure"
+HREF="fileio.html"><LINK
+REL="PREVIOUS"
+TITLE="Mount Table"
+HREF="fileio-mount-table.html"><LINK
+REL="NEXT"
+TITLE="Directories"
+HREF="fileio-directories.html"></HEAD
+><BODY
+CLASS="CHAPTER"
+BGCOLOR="#FFFFFF"
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+SUMMARY="Header navigation table"
+WIDTH="100%"
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+><TH
+COLSPAN="3"
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+>eCos Reference Manual</TH
+></TR
+><TR
+><TD
+WIDTH="10%"
+ALIGN="left"
+VALIGN="bottom"
+><A
+HREF="fileio-mount-table.html"
+ACCESSKEY="P"
+>Prev</A
+></TD
+><TD
+WIDTH="80%"
+ALIGN="center"
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+>Next</A
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+></TABLE
+><HR
+ALIGN="LEFT"
+WIDTH="100%"></DIV
+><DIV
+CLASS="CHAPTER"
+><H1
+><A
+NAME="FILEIO-FILE-TABLE">Chapter 22. File Table</H1
+><P
+>Once a file has been opened it is represented by an open file
+object. These are allocated from an array of available file
+objects. User code accesses these open file objects via a second array
+of pointers which is indexed by small integer offsets. This gives the
+usual Unix file descriptor functionality, complete with the various
+duplication mechanisms.</P
+><P
+>A file table entry has the following structure:</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>struct CYG_FILE_TAG
+{
+ cyg_uint32 f_flag; /* file state */
+ cyg_uint16 f_ucount; /* use count */
+ cyg_uint16 f_type; /* descriptor type */
+ cyg_uint32 f_syncmode; /* synchronization protocol */
+ struct CYG_FILEOPS_TAG *f_ops; /* file operations */
+ off_t f_offset; /* current offset */
+ CYG_ADDRWORD f_data; /* file or socket */
+ CYG_ADDRWORD f_xops; /* extra type specific ops */
+ cyg_mtab_entry *f_mte; /* mount table entry */
+};</PRE
+></TD
+></TR
+></TABLE
+><P
+>The <TT
+CLASS="STRUCTFIELD"
+><I
+>f_flag</I
+></TT
+> field contains some FILEIO
+control bits and some bits propagated from the
+<TT
+CLASS="PARAMETER"
+><I
+>flags</I
+></TT
+> argument of the
+<TT
+CLASS="FUNCTION"
+>open()</TT
+> call (defined by
+<TT
+CLASS="LITERAL"
+>CYG_FILE_MODE_MASK</TT
+>).</P
+><P
+>The <TT
+CLASS="STRUCTFIELD"
+><I
+>f_ucount</I
+></TT
+> field contains a use count that
+controls when a file will be closed. Each duplicate in the file
+descriptor array counts for one reference here. It is also
+incremented around each I/O operation to ensure that the file cannot
+be closed while it has current I/O operations.</P
+><P
+>The <TT
+CLASS="STRUCTFIELD"
+><I
+>f_type</I
+></TT
+> field indicates the type of the
+underlying file object. Some of the possible values here are
+<TT
+CLASS="LITERAL"
+>CYG_FILE_TYPE_FILE</TT
+>,
+<TT
+CLASS="LITERAL"
+>CYG_FILE_TYPE_SOCKET</TT
+> or <TT
+CLASS="LITERAL"
+>CYG_FILE_TYPE_DEVICE</TT
+>.</P
+><P
+>The <TT
+CLASS="STRUCTFIELD"
+><I
+>f_syncmode</I
+></TT
+> field is copied from the
+<TT
+CLASS="STRUCTFIELD"
+><I
+>syncmode</I
+></TT
+> field of the implementing
+filesystem. Its use is described in <A
+HREF="fileio-synchronization.html"
+>Chapter 24</A
+>.</P
+><P
+>The <TT
+CLASS="STRUCTFIELD"
+><I
+>f_offset</I
+></TT
+> field records the current file
+position. It is the responsibility of the file operation functions to
+keep this field up to date.</P
+><P
+>The <TT
+CLASS="STRUCTFIELD"
+><I
+>f_data</I
+></TT
+> field contains private data
+placed here by the underlying filesystem. Normally this will be a
+pointer to, or handle on, the filesystem object that implements this
+file.</P
+><P
+>The <TT
+CLASS="STRUCTFIELD"
+><I
+>f_xops</I
+></TT
+> field contains a pointer to any
+extra type specific operation functions. For example, the socket I/O
+system installs a pointer to a table of functions that implement the
+standard socket operations.</P
+><P
+>The <TT
+CLASS="STRUCTFIELD"
+><I
+>f_mte</I
+></TT
+> field contains a pointer to the
+parent mount table entry for this file. It is used mainly to implement
+the synchronization protocol. This may contain a pointer to some other
+data structure in file objects not derived from a filesystem.</P
+><P
+>The <TT
+CLASS="STRUCTFIELD"
+><I
+>f_ops</I
+></TT
+> field contains a pointer to a
+table of file I/O operations. This has the following structure:</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>struct CYG_FILEOPS_TAG
+{
+ int (*fo_read) (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);
+ int (*fo_write) (struct CYG_FILE_TAG *fp, struct CYG_UIO_TAG *uio);
+ int (*fo_lseek) (struct CYG_FILE_TAG *fp, off_t *pos, int whence );
+ int (*fo_ioctl) (struct CYG_FILE_TAG *fp, CYG_ADDRWORD com,
+ CYG_ADDRWORD data);
+ int (*fo_select) (struct CYG_FILE_TAG *fp, int which, CYG_ADDRWORD info);
+ int (*fo_fsync) (struct CYG_FILE_TAG *fp, int mode );
+ int (*fo_close) (struct CYG_FILE_TAG *fp);
+ int (*fo_fstat) (struct CYG_FILE_TAG *fp, struct stat *buf );
+ int (*fo_getinfo) (struct CYG_FILE_TAG *fp, int key, char *buf, int len );
+ int (*fo_setinfo) (struct CYG_FILE_TAG *fp, int key, char *buf, int len );
+};</PRE
+></TD
+></TR
+></TABLE
+><P
+>It should be obvious from the names of most of these functions what
+their responsibilities are. The <TT
+CLASS="FUNCTION"
+>fo_getinfo()</TT
+>
+and <TT
+CLASS="FUNCTION"
+>fo_setinfo()</TT
+> function pointers, like their
+counterparts in the filesystem structure, implement minor control and
+info functions such as <TT
+CLASS="FUNCTION"
+>fpathconf()</TT
+>.</P
+><P
+>The second argument to the <TT
+CLASS="FUNCTION"
+>fo_read()</TT
+> and
+<TT
+CLASS="FUNCTION"
+>fo_write()</TT
+> function pointers is a pointer to a
+UIO structure:</P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>struct CYG_UIO_TAG
+{
+ struct CYG_IOVEC_TAG *uio_iov; /* pointer to array of iovecs */
+ int uio_iovcnt; /* number of iovecs in array */
+ off_t uio_offset; /* offset into file this uio corresponds to */
+ ssize_t uio_resid; /* residual i/o count */
+ enum cyg_uio_seg uio_segflg; /* see above */
+ enum cyg_uio_rw uio_rw; /* see above */
+};
+
+struct CYG_IOVEC_TAG
+{
+ void *iov_base; /* Base address. */
+ ssize_t iov_len; /* Length. */
+};</PRE
+></TD
+></TR
+></TABLE
+><P
+>This structure encapsulates the parameters of any data transfer
+operation. It provides support for scatter/gather operations and
+records the progress of any data transfer. It is also compatible with
+the I/O operations of any BSD-derived network stacks and filesystems.</P
+><P
+>When a file is opened (or a file object created by some other means,
+such as <TT
+CLASS="FUNCTION"
+>socket()</TT
+> or <TT
+CLASS="FUNCTION"
+>accept()</TT
+>) it is the
+responsibility of the filesystem open operation to initialize all the
+fields of the object except the <TT
+CLASS="STRUCTFIELD"
+><I
+>f_ucount</I
+></TT
+>,
+<TT
+CLASS="STRUCTFIELD"
+><I
+>f_syncmode</I
+></TT
+> and
+<TT
+CLASS="STRUCTFIELD"
+><I
+>f_mte</I
+></TT
+> fields. Since the
+<TT
+CLASS="STRUCTFIELD"
+><I
+>f_flag</I
+></TT
+> field will already contain bits belonging to the FILEIO
+infrastructure, any changes to it must be made with the appropriate
+logical operations.</P
+></DIV
+><DIV
+CLASS="NAVFOOTER"
+><HR
+ALIGN="LEFT"
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+SUMMARY="Footer navigation table"
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