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