fam.3x

好东东。linux下面的文件节点、文件状态的变化监听代码

'\"macro stdmacro
.if n .pH g3x.fam @(#)fam	30.3 of 1/19/86
.nr X
.if \nX=0 .ds x} FAM 3X "Specialized Libraries" "\&"
.if \nX=1 .ds x} FAM 3X "Specialized Libraries"
.if \nX=2 .ds x} FAM 3X "" "\&"
.if \nX=3 .ds x} FAM "" "" "\&"
.TH \*(x}
.SH NAME
fam \- File Alteration Monitor (FAM) library routines
.SH SYNOPSIS
.nf
.B #include <fam.h>
.P
.B "extern int FAMOpen(FAMConnection* fc);"
.PP
.B "extern int FAMClose(FAMConnection* fc);"
.PP
.B "extern int FAMMonitorDirectory(FAMConnection *fc,"
.B "                               char *filename,"
.B "                               FAMRequest* fr,"
.B "                               void* userData);"
.PP
.B "extern int FAMMonitorFile(FAMConnection *fc, 
.B "                          char *filename,"
.B "                          FAMRequest* fr,"
.B "                          void* userData);"
.PP
.B "int FAMSuspendMonitor(FAMConnection *fc, FAMRequest *fr);"
.PP
.B "int FAMResumeMonitor(FAMConnection *fc, FAMRequest *fr);"
.PP
.B "int FAMCancelMonitor(FAMConnection *fc, FAMRequest *fr);"
.PP
.B "int FAMNextEvent(FAMConnection *fc, FAMEvent *fe);"
.PP
.B "int FAMPending(FAMConnection* fc);"
.PP
.B "typedef struct {"
.B "    int fd;"
.B "} FAMConnection;"
.PP
.B "#define FAMCONNECTION_GETFD(fc)      (fc->fd)"
.PP
.B "typedef struct {"
.B "    int reqnum;"
.B "} FAMRequest;"
.PP
.B "enum FAMCodes { FAMChanged=1, FAMDeleted=2, FAMStartExecuting=3, "
.B "    FAMStopExecuting=4, FAMCreated=5, FAMMoved=6, FAMAcknowledge=7,"
.B "    FAMExists=8, FAMEndExist=9 };"
.PP
.B "typedef struct {"
.B "    FAMConnection* fc;"
.B "    FAMRequest fr;"
.B "    char hostname[MAXHOSTNAMELEN];"
.B "    char filename[NAME_MAX];"
.B "    void *userdata;"
.B "    FAMCodes code;"
.B "} FAMEvent;"
.PP
.B "extern int FAMErrno;"
.PP
.B "extern char *FamErrlist[];"
.PP
.SH DESCRIPTION
\fIFAM\fP monitors files and directories, notifying interested
applications of changes.  Routines for communicating with the fam(1M)
server process are found in ``libfam.a'', which is loaded if the
option ``-lfam'' is used with cc(1) or ld(1).  The library
``libC.a'' (``-lC'') must also be specified.
.PP
An application calls routines described here to establish a list of
files for \fIfam \fPto monitor.  \fIFam \fPgenerates events on a socket to
communicate with the application.  The \fIfam\fP process is started when
the first connection from any application to it is opened.  It exits
after all connections to it have been closed.
.PP
.SH USING FAM
Here are the steps required to use \fIFAM \fPin an application:
.PP
.AL
.LI
.IP 1.
Create a connection to \fIfam\fP by calling FAMOpen.  This routine
will pass back a FAMConnection structure used in all \fIfam \fP
procedures. 
.IP 2.
Tell \fIfam\fP which files and directories to monitor by calling
FAMMonitorFile and FAMMonitorDirectory to express interest in
files and directories, respectively.
.IP 3.
Select on the \fIfam\fP socket file descriptor and call
FAMPending when the \fIfam \fPsocket is active, and FAMNextEvent when
FAMPending indicates that an event is available.  Alternatively,
call FAMPending (or FAMNextEvent)
periodically to check the socket connection to \fIfam\fP to see
if any new information has arrived.  If there are no events
pending, FAMNextEvent blocks until an event occurs.
.IP 4.
When the application is through monitoring a file or directory, it
should call FAMCancelMonitor.  If the application wants to
temporarily suspend monitoring of a file or directory, it may call
FAMSuspendMonitor.  When the application is ready to start
monitoring again, it calls FAMResumeMonitor.
.IP 5.
Before the application exits, it should call FAMClose to free
resources associated with files still being monitored and to close the
connection to \fIfam.\fP
.PP
.SH DATA STRUCTURES
.B "The FAMConnection Structure"
.PP
The FAMConnection data structure is created when opening a connection
to \fIFAM.\fP  Subsequently it is passed into all \fIFAM \fPprocedures.  This
structure has all the information in it to communicate to \fIfam\fP.
.PP
Use the macro FAMCONNECTION_GETFD to access the file descriptor inside the
FAMConnection, rather than accessing it directly.
.PP
.B "The FAMRequest Structure"
.PP
When \fIfam\fP is called on to monitor a file, it passes back a
FAMRequest structure.  This structure uniquely identifies the request
so that it may be cancelled, using FAMCancelMonitor
or suspended, using FAMSuspendMonitor.
.PP
.B "The FAMEvent Structure"
.PP
Changes to files and directories are encoded in the FAMEvent
structure.  The \fIcode \fPfield of this structure contains one of the
following enumeration constants:
.TP .90i
.SM FAMChanged
Some value which can be obtained with fstat(1) changed for a file or
directory being monitored.
.TP
.SM FAMDeleted
A file or directory being monitored was deleted or its name was changed.
This event is also generated when monitoring starts on a nonexistent file or directory.
.TP
.SM FAMStartExecuting
An executable file or shared library
being monitored started executing.  If multiple processes execute
the same file, this event only occurs when the first process starts.
.TP
.SM FAMStopExecuting
An executable file being monitored which was running finished.  If
multiple processes from an executable are running, this event is only
generated when the last one finishes.
.TP
.SM FAMCreated
A file was created in a directory being monitored.  Note: this event
is only generated for files created directly in a directory being
monitored; subdirectories are not automatically monitored.
.TP
.SM FAMMoved
FAMMoved events never occur.  The name remains defined so that
programs that reference it will still compile.
.TP
.SM FAMAcknowledge
After a FAMCancelMonitor, \fIfam \fPgenerates a FAMAcknowledge event.
Also, if an invalid pathname is specified, \fIfam \fP generates a
FAMAcknowledge event.
.TP
.SM FAMExists
When the application requests a file be monitored, \fIfam\fP
generates a FAMExists event for that file.  When the application
requests a directory be monitored, \fIfam\fP generates a FAMExists
event for that directory and every file directly contained in that
directory.
.TP
.SM FAMEndExist
When the application requests a file directory be monitored, a series of
FAMExists events is generated as described above.  After the last
FAMExists message, \fIfam \fPgenerates a FAMEndExist message.
.PP
If a FAM event applies to a file or directory being monitored, the
FAMEvent's \fIfilename \fPfield contains the full pathname
that was passed to fam.
If an event applies to an entry in a monitored directory, the
\fIfilename \fPfield contains the relative path only.  For
example, if the directory \fI/usr/tmp/xyzzy \fPwere monitored,
and the file \fI/usr/tmp/xyzzy/plugh \fP were deleted, a FAMDeleted
event would be generated containing "plugh" in \fIfilename\fP.
If the directory itself were deleted, \fIfilename \fPwould contain
"/usr/tmp/xyzzy".
.\".SH ERROR HANDLING
.\"If an error occurs inside of \fIFAM, \fPa global named FAMErrno is set to a
.\"non-zero value and the routine that generated the error in will return an error
.\"value.  The value of FAMErrno is valid until the next \fIFAM \fProutine is
.\"called.  The FAMErrno can be translated in to a character string using the
.\"global array FAMErrlist.
.PP
.SH PROCEDURES

.B "FAMOpen, FAMClose"
.PP
The application opens a connection to \fIfam \fPby calling FAMOpen.  FAMOpen
initializes the FAMConnection structure passed in to it and returns 0 if
successful, otherwise -1.  The variable char* appName should be set to the 
name of your application. The FAMConnection structure is passed to all
subsequent \fIFAM \fPprocedure calls.

FAMClose frees resources associated with files still being monitored and closes
a \fIfam \fPconnection.  It returns 0 if successful and -1 otherwise.
.PP
.B "FAMMonitorDirectory, FAMMonitorFile"
.PP
FAMMonitorDirectory and FAMMonitorFile tell \fIFAM \fPto start
monitoring a directory or file, respectively.  The parameters to this
function are a FAMConnection (initialized by FAMOpen), a FAMRequest
structure, a filename and a user data pointer.  The FAMRequest
structure is modified to subsequently identify this request.  When
the file or directory changes, a \fIFAM \fPevent structure will be
generated.  The application can retrieve this structure by calling
FAMNextEvent (see description under FAMNextEvent).
.PP
FAMMonitorDirectory monitors changes that happens to the contents of the
directory (as well as the directory file itself); FAMMonitorFile monitors only
what happens to a particular file.  Both routines return 0 if successful and -1
otherwise.
.PP
The filename argument must be a full pathname.

.B "FAMSuspendMonitor, FAMResumeMonitor"
.PP
FAMSuspendMonitor temporarily suspends monitoring of files or directories.
This is useful when an application is not displaying information about files,
when it is iconified, for example.  FAMResumeMonitor signals \fIfam \fPto
start monitoring the file or directory again.  Changes which occur while
monitoring is suspended are enqueued and delivered when monitoring is
resumed.
.PP
Both of these routines take a FAMConnection and a FAMRequest structure.
The FAMRequest Structure is returned from the FAMMonitorFile or
FAMMonitorDirectory routines and return 0 if successful and -1 otherwise.
.PP
Because fam runs as an asynchronous process, FAMNextEvent may return
a few events regarding a given request after that request has been suspended.

.B "FAMCancelMonitor"
.PP
When an application is through monitoring a file or directory, it should
call FAMCancelMonitor.  This routine will signal \fIfam \fPnot to monitor
this directory anymore.  The FAMRequest structure is returned from the
FAMMonitorFile or FAMMonitorDirectory routines.  FAMCancelMonitor returns 0 if
successful and -1 otherwise.
.PP

.B "FAMPending, FAMNextEvent"
.PP
FAMPending returns 1 if an event is waiting and 0 if no event is waiting.  It
also returns 1 if an error has been encountered.  This routine returns
immediately to the caller.
.PP
FAMNextEvent will get the next \fIFAM \fPevent.  If there are no \fIFAM
\fPevents waiting, then the calling application blocks until a \fIFAM \fPevent
is received.  If blocking is not desirable, call FAMPending before
FAMNextEvent, and only call FAMNextEvent when FAMPending says an event is
available.
.PP
There are two ways to for applications to receive \fIFAM \fPevents:
.PP
.AL
.LI
1. The Select approach - The application selects on the file
    descriptor returned from FAMOpen, in the FAMConnection structure.
    When this file descriptor becomes active, the application calls
    FAMPending to determine whether a complete event is ready, and
    FAMNextEvent to retrieve the pending \fIFAM \fPevent.
.PP
2. The Polling approach - The application calls FAMPending
    periodically (usually when the system is waiting for input).
    When FAMPending returns 1, the application calls FAMNextEvent to
    retrieve the pending \fIFAM \fP event.
.PP
FAMNextEvent reads any information that is on the \fIfam \fPsocket,
and returns it to the application in the form of a FAMEvent.
.PP
FAMNextEvent returns 1 if successful and -1 otherwise.


.SH SEE ALSO
fam(1M).
.SH BUGS
The FAMMoved event is not currently supported.
.PP
FAMNextEvent may not initialize the FAMEvent's filename field
for FAMEndExist and FAMAcknowledge events.
Use the request number to determine the file or directory
to which those events refer.
.PP
FAMErrno and FamErrlist are not set when errors occur.
.PP
When a shell script is run, notification is generated for the shell
executing the script, typically sh(1) or csh(1).
.PP
Each process is limited to 1000 active requests at a time.