Provided by: libfam-dev_2.7.0-17.2_amd64 
NAME
fam - File Alteration Monitor (FAM) library routines
SYNOPSIS
#include <fam.h>
extern int FAMOpen(FAMConnection* fc);
extern int FAMOpen2(FAMConnection* fc,
const char* appName);
extern int FAMClose(FAMConnection* fc);
extern int FAMMonitorDirectory(FAMConnection *fc,
char *filename,
FAMRequest* fr,
void* userData);
extern int FAMMonitorFile(FAMConnection *fc,
char *filename,
FAMRequest* fr,
void* userData);
int FAMSuspendMonitor(FAMConnection *fc, FAMRequest *fr);
int FAMResumeMonitor(FAMConnection *fc, FAMRequest *fr);
int FAMCancelMonitor(FAMConnection *fc, FAMRequest *fr);
int FAMNextEvent(FAMConnection *fc, FAMEvent *fe);
int FAMPending(FAMConnection* fc);
typedef struct {
int fd;
} FAMConnection;
#define FAMCONNECTION_GETFD(fc) (fc->fd)
typedef struct {
int reqnum;
} FAMRequest;
enum FAMCodes { FAMChanged=1, FAMDeleted=2, FAMStartExecuting=3,
FAMStopExecuting=4, FAMCreated=5, FAMMoved=6, FAMAcknowledge=7,
FAMExists=8, FAMEndExist=9 };
typedef struct {
FAMConnection* fc;
FAMRequest fr;
char hostname[MAXHOSTNAMELEN];
char filename[NAME_MAX];
void *userdata;
FAMCodes code;
} FAMEvent;
extern int FAMErrno;
extern char *FamErrlist[];
DESCRIPTION
FAM, the File Alteration Monitor, is a subsystem that applications can use to be notified
when specific files or directories are changed. It is intended as a replacement for
mechanisms such as poll and select.
FAM comes in two parts: famd, the daemon that listens for requests and provides
notifications, and libfam a library that client applications can use to communicate with
FAM.
libfam's routines are found in libfam.a, which is loaded if the option -lfam is used with
cc or ld.
An application calls routines described here to establish a list of files for famdto
monitor. famdgenerates events on a socket to communicate with the application. The famd
process is started when the first connection from any application to it is opened. It
exits after all connections to it have been closed.
USAGE
Here are the steps required to use FAM in an application:
1. Create a connection to famd by calling FAMOpen. This routine will pass back a
FAMConnection structure used in all FAM procedures.
2. Tell famd which files and directories to monitor by calling FAMMonitorFile and
FAMMonitorDirectory to express interest in files and directories, respectively.
3. Select on the famd socket file descriptor and call FAMPending when the famd socket
is active, and FAMNextEvent when FAMPending indicates that an event is available.
Alternatively, call FAMPending (or FAMNextEvent) periodically to check the socket
connection to famd to see if any new information has arrived. If there are no
events pending, FAMNextEvent blocks until an event occurs.
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.
5. Before the application exits, it should call FAMClose to free resources associated
with files still being monitored and to close the connection to famd.
DATA STRUCTURES
The FAMConnection Structure
The FAMConnection data structure is created when opening a connection to famd.
Subsequently it is passed into all FAM procedures. This structure has all the information
in it to communicate to fam.
Use the macro FAMCONNECTION_GETFD to access the file descriptor inside the FAMConnection,
rather than accessing it directly.
The FAMRequest Structure
When famd 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.
The FAMEvent Structure
Changes to files and directories are encoded in the FAMEvent structure. The code field of
this structure contains one of the following enumeration constants:
FAMChanged
Some value which can be obtained with fstat changed for a file or directory being
monitored.
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.
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.
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.
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.
FAMMoved FAMMoved events never occur. The name remains defined so that programs that
reference it will still compile.
FAMAcknowledge
After a FAMCancelMonitor, famd generates a FAMAcknowledge event. Also, if an
invalid pathname is specified, famd generates a FAMAcknowledge event.
FAMExists
When the application requests a file be monitored, famd generates a FAMExists
event for that file. When the application requests a directory be monitored,
famd generates a FAMExists event for that directory and every file directly
contained in that directory.
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, famd generates a FAMEndExist message.
If a FAM event applies to a file or directory being monitored, the FAMEvent's filename
field contains the full pathname that was passed to famd. If an event applies to an entry
in a monitored directory, the filename field contains the relative path only. For
example, if the directory /tmp/xyzzy were monitored, and the file /tmp/xyzzy/plugh were
deleted, a FAMDeleted event would be generated containing "plugh" in filename. If the
directory itself were deleted, filename would contain "/tmp/xyzzy".
PROCEDURES
FAMOpen, FAMClose
The application opens a connection to famd by calling FAMOpen. FAMOpen initializes the
FAMConnection structure passed in to it and returns 0 if successful, otherwise -1. The
parameter appName of FAMOpen2 should be set to the name of your application. The
FAMConnection structure is passed to all subsequent FAM procedure calls.
FAMClose frees resources associated with files still being monitored and closes a famd
connection. It returns 0 if successful and -1 otherwise.
FAMMonitorDirectory, FAMMonitorFile
FAMMonitorDirectory and FAMMonitorFile tell famd to 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 FAM event structure will be generated. The application can retrieve this
structure by calling FAMNextEvent (see description under FAMNextEvent).
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.
The filename argument must be a full pathname.
FAMSuspendMonitor, FAMResumeMonitor
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 famd to start monitoring the file or directory again.
Changes which occur while monitoring is suspended are enqueued and delivered when
monitoring is resumed.
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.
Because famd runs as an asynchronous process, FAMNextEvent may return a few events
regarding a given request after that request has been suspended.
FAMCancelMonitor
When an application is finished monitoring a file or directory, it should call
FAMCancelMonitor. This routine will signal famd not to monitor this directory anymore.
The FAMRequest structure is returned from the FAMMonitorFile or FAMMonitorDirectory
routines. FAMCancelMonitor returns 0 if successful and -1 otherwise.
FAMPending, FAMNextEvent
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.
FAMNextEvent will get the next FAM event. If there are no FAM events waiting, then the
calling application blocks until a FAM event is received. If blocking is not desirable,
call FAMPending before FAMNextEvent, and only call FAMNextEvent when FAMPending says an
event is available.
There are two ways to for applications to receive FAM events:
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 FAM event.
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 FAM event.
FAMNextEvent reads any information that is on the famd socket, and returns it to the
application in the form of a FAMEvent.
FAMNextEvent returns 1 if successful and -1 otherwise.
SEE ALSO
famd(8), fstat(2), poll(2), select(2)
BUGS
The FAMMoved event is not currently supported.
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.
FAMErrno and FamErrlist are not set when errors occur.
When a shell script is run, notification is generated for the shell executing the script.
Each process is limited to 1000 active requests at a time.
When using the Linux DNotify kernel monitor, a file handle will be opened for each file
famd is asked to monitor, meaning the file system the file resides on can not be
unmounted.