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><A
NAME="FILEIO-SYNCHRONIZATION">Chapter 24. Synchronization</H1
><P
>The FILEIO infrastructure provides a synchronization mechanism for
controlling concurrent access to filesystems. This allows existing
filesystems to be ported to eCos, even if they do not have their own
synchronization mechanisms. It also allows new filesystems to be
implemented easily without having to consider the synchronization
issues.</P
><P
>The infrastructure maintains a mutex for each entry in each of
the main tables: filesystem table, mount table and file table. For
each class of operation each of these mutexes may be locked before the
corresponding filesystem operation is invoked.</P
><P
>The synchronization protocol required by a filesystem is described
by the <TT
CLASS="STRUCTFIELD"
><I
>syncmode</I
></TT
> field of the filesystem
table entry. This is a combination of the following flags:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>CYG_SYNCMODE_FILE_FILESYSTEM</TT
></DT
><DD
><P
>Lock the filesystem table entry mutex
during all filesystem level operations.</P
></DD
><DT
><TT
CLASS="LITERAL"
>CYG_SYNCMODE_FILE_MOUNTPOINT</TT
></DT
><DD
><P
>Lock the mount table entry mutex
during all filesystem level operations.</P
></DD
><DT
><TT
CLASS="LITERAL"
>CYG_SYNCMODE_IO_FILE</TT
></DT
><DD
><P
>Lock the file table entry mutex during all
I/O operations.</P
></DD
><DT
><TT
CLASS="LITERAL"
>CYG_SYNCMODE_IO_FILESYSTEM</TT
></DT
><DD
><P
>Lock the filesystem table entry mutex during all I/O operations.</P
></DD
><DT
><TT
CLASS="LITERAL"
>CYG_SYNCMODE_IO_MOUNTPOINT</TT
></DT
><DD
><P
>Lock the mount table entry mutex during all I/O operations.</P
></DD
><DT
><TT
CLASS="LITERAL"
>CYG_SYNCMODE_SOCK_FILE</TT
></DT
><DD
><P
>Lock the file table entry mutex during all socket operations.</P
></DD
><DT
><TT
CLASS="LITERAL"
>CYG_SYNCMODE_SOCK_NETSTACK</TT
></DT
><DD
><P
>Lock the network stack table entry mutex during all socket operations.</P
></DD
><DT
><TT
CLASS="LITERAL"
>CYG_SYNCMODE_NONE</TT
></DT
><DD
><P
>Perform no locking at all during any operations.</P
></DD
></DL
></DIV
><P
>The value of the <TT
CLASS="STRUCTFIELD"
><I
>syncmode</I
></TT
> field in the
filesystem table entry will be copied by the infrastructure to the
open file object after a successful <TT
CLASS="FUNCTION"
>open()</TT
> operation.</P
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