Keywords: developers

Subsections

- newPlugin(bpContext *ctx)
- freePlugin(bpContext *ctx)
- getPluginValue(bpContext *ctx, pVariable var, void *value)
- setPluginValue(bpContext *ctx, pVariable var, void *value)
- handlePluginEvent(bpContext *ctx, bEvent *event, void *value)
- startBackupFile(bpContext *ctx, struct save_pkt *sp)
- endBackupFile(bpContext *ctx)
- startRestoreFile(bpContext *ctx, const char *cmd)
- createFile(bpContext *ctx, struct restore_pkt *rp)
- setFileAttributes(bpContext *ctx, struct restore_pkt *rp)
- endRestoreFile(bpContext *ctx)
- pluginIO(bpContext *ctx, struct io_pkt *io)
- bool checkFile(bpContext *ctx, char *fname)

# Plugin Entry Points

This section will describe each of the entry points (subroutines) within the plugin that the plugin must provide for Bacula, when they are called and their arguments. As noted above, pointers to these subroutines are passed back to Bacula in the pFuncs structure when Bacula calls the loadPlugin() externally defined entry point.

## newPlugin(bpContext *ctx)

This is the entry point that Bacula will call when a new "instance" of the plugin is created. This typically happens at the beginning of a Job. If 10 Jobs are running simultaneously, there will be at least 10 instances of the plugin.

The bpContext structure will be passed to the plugin, and during this call, if the plugin needs to have its private working storage that is associated with the particular instance of the plugin, it should create it from the heap (malloc the memory) and store a pointer to its private working storage in the pContext variable. Note: since Bacula is a multi-threaded program, you must not keep any variable data in your plugin unless it is truly meant to apply globally to the whole plugin. In addition, you must be aware that except the first and last call to the plugin (loadPlugin and unloadPlugin) all the other calls will be made by threads that correspond to a Bacula job. The bpContext that will be passed for each thread will remain the same throughout the Job thus you can keep your private Job specific data in it (bContext).

    typedef struct s_bpContext {
      void *pContext;   /* Plugin private context */
      void *bContext;   /* Bacula private context */
    } bpContext;

This context pointer will be passed as the first argument to all the entry points that Bacula calls within the plugin. Needless to say, the plugin should not change the bContext variable, which is Bacula's private context pointer for this instance (Job) of this plugin.

## freePlugin(bpContext *ctx)

This entry point is called when the this instance of the plugin is no longer needed (the Job is ending), and the plugin should release all memory it may have allocated for this particular instance (Job) i.e. the pContext. This is not the final termination of the plugin signaled by a call to unloadPlugin. Any other instances (Job) will continue to run, and the entry point newPlugin may be called again if other jobs start.

## getPluginValue(bpContext *ctx, pVariable var, void *value)

Bacula will call this entry point to get a value from the plugin. This entry point is currently not called.

## setPluginValue(bpContext *ctx, pVariable var, void *value)

Bacula will call this entry point to set a value in the plugin. This entry point is currently not called.

## handlePluginEvent(bpContext *ctx, bEvent *event, void *value)

This entry point is called when Bacula encounters certain events (discussed below). This is, in fact, the main way that most plugins get control when a Job runs and how they know what is happening in the job. It can be likened to the RunScript feature that calls external programs and scripts, and is very similar to the Bacula Python interface. When the plugin is called, Bacula passes it the pointer to an event structure (bEvent), which currently has one item, the eventType:

    typedef struct s_bEvent {
       uint32_t eventType;
    } bEvent;

which defines what event has been triggered, and for each event, Bacula will pass a pointer to a value associated with that event. If no value is associated with a particular event, Bacula will pass a NULL pointer, so the plugin must be careful to always check value pointer prior to dereferencing it.

The current list of events are:

    typedef enum {
      bEventJobStart                        = 1,
      bEventJobEnd                          = 2,
      bEventStartBackupJob                  = 3,
      bEventEndBackupJob                    = 4,
      bEventStartRestoreJob                 = 5,
      bEventEndRestoreJob                   = 6,
      bEventStartVerifyJob                  = 7,
      bEventEndVerifyJob                    = 8,
      bEventBackupCommand                   = 9,
      bEventRestoreCommand                  = 10,
      bEventLevel                           = 11,
      bEventSince                           = 12,
      bEventCancelCommand                   = 13,  /* Executed by another thread */

      /* Just before bEventVssPrepareSnapshot */
      bEventVssBackupAddComponents          = 14,

      bEventVssRestoreLoadComponentMetadata = 15,
      bEventVssRestoreSetComponentsSelected = 16,
      bEventRestoreObject                   = 17,
      bEventEndFileSet                      = 18,
      bEventPluginCommand                   = 19,
      bEventVssBeforeCloseRestore           = 21,

      /* Add drives to VSS snapshot
       *  argument: char[27] drivelist
       * You need to add them without duplicates,
       * see fd_common.h add_drive() copy_drives() to get help
       */
      bEventVssPrepareSnapshot              = 22,
      bEventOptionPlugin                    = 23,
      bEventHandleBackupFile                = 24 /* Used with Options Plugin */

    } bEventType;

Most of the above are self-explanatory.

bEventJobStart
  is called whenever a Job starts. The value passed is a pointer to a string that contains: "Jobid=nnn Job=job-name". Where nnn will be replaced by the JobId and job-name will be replaced by the Job name. The variable is temporary so if you need the values, you must copy them.

bEventJobEnd
  is called whenever a Job ends. No value is passed.

bEventStartBackupJob
  is called when a Backup Job begins. No value is passed.

bEventEndBackupJob
  is called when a Backup Job ends. No value is passed.

bEventStartRestoreJob
  is called when a Restore Job starts. No value is passed.

bEventEndRestoreJob
  is called when a Restore Job ends. No value is passed.

bEventStartVerifyJob
  is called when a Verify Job starts. No value is passed.

bEventEndVerifyJob
  is called when a Verify Job ends. No value is passed.

bEventBackupCommand
  is called prior to the bEventStartBackupJob and the plugin is passed the command string (everything after the equal sign in "Plugin =" as the value.

  Note, if you intend to backup a file, this is an important first point to write code that copies the command string passed into your pContext area so that you will know that a backup is being performed and you will know the full contents of the "Plugin =" command (i.e. what to backup and what virtual filename the user wants to call it.

bEventRestoreCommand
  is called prior to the bEventStartRestoreJob and the plugin is passed the command string (everything after the equal sign in "Plugin =" as the value.

  See the notes above concerning backup and the command string. This is the point at which Bacula passes you the original command string that was specified during the backup, so you will want to save it in your pContext area for later use when Bacula calls the plugin again.

bEventLevel
  is called when the level is set for a new Job. The value is a 32 bit integer stored in the void*, which represents the Job Level code.

bEventSince
  is called when the since time is set for a new Job. The value is a time_t time at which the last job was run.

bEventCancelCommand
  is called whenever the currently running Job is cancelled. Be warned that this event is sent by a different thread.

bEventVssBackupAddComponents

bEventPluginCommand
  is called for each PluginCommand present in the current FileSet. The event will be sent only on plugin specifed in the command. The argument is the PluginCommand (not valid after the call).

bEventHandleBackupFile
  is called for each file of a FileSet when using a Options Plugin. If the plugin returns CF_OK, it will be used for the backup, if it returns CF_SKIP, the file will be skipped. Anything else will backup the file with Bacula core functions.

During each of the above calls, the plugin receives either no specific value or only one value, which in some cases may not be sufficient. However, knowing the context of the event, the plugin can call back to the Bacula entry points it was passed during the loadPlugin call and get to a number of Bacula variables. (at the current time few Bacula variables are implemented, but it easily extended at a future time and as needs require).

## startBackupFile(bpContext *ctx, struct save_pkt *sp)

This entry point is called only if your plugin is a command plugin, and it is called when Bacula encounters the "Plugin = " directive in the Include section of the FileSet. Called when beginning the backup of a file. Here Bacula provides you with a pointer to the save_pkt structure and you must fill in this packet with the "attribute" data of the file.

    struct save_pkt {
       int32_t pkt_size;                  /* size of this packet */
       char *fname;                       /* Full path and filename */
       char *link;                        /* Link name if any */
       struct stat statp;                 /* System stat() packet for file */
       int32_t type;                      /* FT_xx for this file */
       uint32_t flags;                    /* Bacula internal flags */
       bool portable;                     /* set if data format is portable */
       char *cmd;                         /* command */
       uint32_t delta_seq;                /* Delta sequence number */
       char *object_name;                 /* Object name to create */
       char *object;                      /* restore object data to save */
       int32_t object_len;                /* restore object length */
       int32_t index;                     /* restore object index */
       int32_t pkt_end;                   /* end packet sentinel */
    };

The second argument is a pointer to the save_pkt structure for the file to be backed up. The plugin is responsible for filling in all the fields of the save_pkt. If you are backing up a real file, then generally, the statp structure can be filled in by doing a stat system call on the file.

If you are backing up a database or something that is more complex, you might want to create a virtual file. That is a file that does not actually exist on the filesystem, but represents say an object that you are backing up. In that case, you need to ensure that the fname string that you pass back is unique so that it does not conflict with a real file on the system, and you need to artifically create values in the statp packet.

Example programs such as bpipe-fd.c show how to set these fields. You must take care not to store pointers the stack in the pointer fields such as fname and link, because when you return from your function, your stack entries will be destroyed. The solution in that case is to malloc() and return the pointer to it. In order to not have memory leaks, you should store a pointer to all memory allocated in your pContext structure so that in subsequent calls or at termination, you can release it back to the system.

Once the backup has begun, Bacula will call your plugin at the pluginIO entry point to "read" the data to be backed up. Please see the bpipe-fd.c plugin for how to do I/O.

Example of filling in the save_pkt as used in bpipe-fd.c:

       struct plugin_ctx *p_ctx = (struct plugin_ctx *)ctx->pContext;
       time_t now = time(NULL);
       sp->fname = p_ctx->fname;
       sp->statp.st_mode = 0700 | S_IFREG;
       sp->statp.st_ctime = now;
       sp->statp.st_mtime = now;
       sp->statp.st_atime = now;
       sp->statp.st_size = -1;
       sp->statp.st_blksize = 4096;
       sp->statp.st_blocks = 1;
       p_ctx->backup = true;
       return bRC_OK;

Note: the filename to be created has already been created from the command string previously sent to the plugin and is in the plugin context (p_ctx->fname) and is a malloc()ed string. This example creates a regular file (S_IFREG), with various fields being created.

In general, the sequence of commands issued from Bacula to the plugin to do a backup while processing the "Plugin = " directive are:

1. generate a bEventBackupCommand event to the specified plugin and pass it the command string.
2. make a startPluginBackup call to the plugin, which fills in the data needed in save_pkt to save as the file attributes and to put on the Volume and in the catalog.
3. call Bacula's internal save_file() subroutine to save the specified file. The plugin will then be called at pluginIO() to "open" the file, and then to read the file data. Note, if you are dealing with a virtual file, the "open" operation is something the plugin does internally and it doesn't necessarily mean opening a file on the filesystem. For example in the case of the bpipe-fd.c program, it initiates a pipe to the requested program. Finally when the plugin signals to Bacula that all the data was read, Bacula will call the plugin with the "close" pluginIO() function.

## endBackupFile(bpContext *ctx)

Called at the end of backing up a file for a command plugin. If the plugin's work is done, it should return bRC_OK. If the plugin wishes to create another file and back it up, then it must return bRC_More (not yet implemented). This is probably a good time to release any malloc()ed memory you used to pass back filenames.

## startRestoreFile(bpContext *ctx, const char *cmd)

Called when the first record is read from the Volume that was previously written by the command plugin.

## createFile(bpContext *ctx, struct restore_pkt *rp)

Called for a command plugin to create a file during a Restore job before restoring the data. This entry point is called before any I/O is done on the file. After this call, Bacula will call pluginIO() to open the file for write.

The data in the restore_pkt is passed to the plugin and is based on the data that was originally given by the plugin during the backup and the current user restore settings (e.g. where, RegexWhere, replace). This allows the plugin to first create a file (if necessary) so that the data can be transmitted to it. The next call to the plugin will be a pluginIO command with a request to open the file write-only.

This call must return one of the following values:

     enum {
       CF_SKIP = 1,       /* skip file (not newer or something) */
       CF_ERROR,          /* error creating file */
       CF_EXTRACT,        /* file created, data to extract */
       CF_CREATED,        /* file created, no data to extract */
       CF_CORE            /* let bacula core handles the file creation */
    };

in the restore_pkt value create_status. For a normal file, unless there is an error, you must return CF_EXTRACT.

    struct restore_pkt {
       int32_t pkt_size;                  /* size of this packet */
       int32_t stream;                    /* attribute stream id */
       int32_t data_stream;               /* id of data stream to follow */
       int32_t type;                      /* file type FT */
       int32_t file_index;                /* file index */
       int32_t LinkFI;                    /* file index to data if hard link */
       uid_t uid;                         /* userid */
       struct stat statp;                 /* decoded stat packet */
       const char *attrEx;                /* extended attributes if any */
       const char *ofname;                /* output filename */
       const char *olname;                /* output link name */
       const char *where;                 /* where */
       const char *RegexWhere;            /* regex where */
       int replace;                       /* replace flag */
       int create_status;                 /* status from createFile() */
       int32_t pkt_end;                   /* end packet sentinel */

    };

Typical code to create a regular file would be the following:

       struct plugin_ctx *p_ctx = (struct plugin_ctx *)ctx->pContext;
       time_t now = time(NULL);
       sp->fname = p_ctx->fname;   /* set the full path/filename I want to create */
       sp->type = FT_REG;
       sp->statp.st_mode = 0700 | S_IFREG;
       sp->statp.st_ctime = now;
       sp->statp.st_mtime = now;
       sp->statp.st_atime = now;
       sp->statp.st_size = -1;
       sp->statp.st_blksize = 4096;
       sp->statp.st_blocks = 1;
       return bRC_OK;

This will create a virtual file. If you are creating a file that actually exists, you will most likely want to fill the statp packet using the stat() system call.

Creating a directory is similar, but requires a few extra steps:

       struct plugin_ctx *p_ctx = (struct plugin_ctx *)ctx->pContext;
       time_t now = time(NULL);
       sp->fname = p_ctx->fname;   /* set the full path I want to create */
       sp->link = xxx; where xxx is p_ctx->fname with a trailing forward slash
       sp->type = FT_DIREND
       sp->statp.st_mode = 0700 | S_IFDIR;
       sp->statp.st_ctime = now;
       sp->statp.st_mtime = now;
       sp->statp.st_atime = now;
       sp->statp.st_size = -1;
       sp->statp.st_blksize = 4096;
       sp->statp.st_blocks = 1;
       return bRC_OK;

The link field must be set with the full cononical path name, which always ends with a forward slash. If you do not terminate it with a forward slash, you will surely have problems later.

As with the example that creates a file, if you are backing up a real directory, you will want to do an stat() on the directory.

Note, if you want the directory permissions and times to be correctly restored, you must create the directory after all the file directories have been sent to Bacula. That allows the restore process to restore all the files in a directory using default directory options, then at the end, restore the directory permissions. If you do it the other way around, each time you restore a file, the OS will modify the time values for the directory entry.

## setFileAttributes(bpContext *ctx, struct restore_pkt *rp)

This is call not yet implemented. Called for a command plugin.

See the definition of restre_pkt in the above section.

## endRestoreFile(bpContext *ctx)

Called when a command plugin is done restoring a file.

## pluginIO(bpContext *ctx, struct io_pkt *io)

Called to do the input (backup) or output (restore) of data from or to a file for a command plugin. These routines simulate the Unix read(), write(), open(), close(), and lseek() I/O calls, and the arguments are passed in the packet and the return values are also placed in the packet. In addition for Win32 systems the plugin must return two additional values (described below).

     enum {
       IO_OPEN = 1,
       IO_READ = 2,
       IO_WRITE = 3,
       IO_CLOSE = 4,
       IO_SEEK = 5
    };

    struct io_pkt {
       int32_t pkt_size;                  /* Size of this packet */
       int32_t func;                      /* Function code */
       int32_t count;                     /* read/write count */
       mode_t mode;                       /* permissions for created files */
       int32_t flags;                     /* Open flags */
       char *buf;                         /* read/write buffer */
       const char *fname;                 /* open filename */
       int32_t status;                    /* return status */
       int32_t io_errno;                  /* errno code */
       int32_t lerror;                    /* Win32 error code */
       int32_t whence;                    /* lseek argument */
       boffset_t offset;                  /* lseek argument */
       bool win32;                        /* Win32 GetLastError returned */
       int32_t pkt_end;                   /* end packet sentinel */
    };

The particular Unix function being simulated is indicated by the func, which will have one of the IO_OPEN, IO_READ, ... codes listed above. The status code that would be returned from a Unix call is returned in status for IO_OPEN, IO_CLOSE, IO_READ, and IO_WRITE. The return value for IO_SEEK is returned in offset which in general is a 64 bit value.

When there is an error on Unix systems, you must always set io_error, and on a Win32 system, you must always set win32, and the returned value from the OS call GetLastError() in lerror.

For all except IO_SEEK, status is the return result. In general it is a positive integer unless there is an error in which case it is -1.

The following describes each call and what you get and what you should return:

IO_OPEN
  You will be passed fname, mode, and flags. You must set on return: status, and if there is a Unix error io_errno must be set to the errno value, and if there is a Win32 error win32 and lerror.

IO_READ
  You will be passed: count, and buf (buffer of size count). You must set on return: status to the number of bytes read into the buffer (buf) or -1 on an error, and if there is a Unix error io_errno must be set to the errno value, and if there is a Win32 error, win32 and lerror must be set.

IO_WRITE
  You will be passed: count, and buf (buffer of size count). You must set on return: status to the number of bytes written from the buffer (buf) or -1 on an error, and if there is a Unix error io_errno must be set to the errno value, and if there is a Win32 error, win32 and lerror must be set.

IO_CLOSE
  Nothing will be passed to you. On return you must set status to 0 on success and -1 on failure. If there is a Unix error io_errno must be set to the errno value, and if there is a Win32 error, win32 and lerror must be set.

IO_LSEEK
  You will be passed: offset, and whence. offset is a 64 bit value and is the position to seek to relative to whence. whence is one of the following SEEK_SET, SEEK_CUR, or SEEK_END indicating to either to seek to an absolute possition, relative to the current position or relative to the end of the file. You must pass back in offset the absolute location to which you seeked. If there is an error, offset should be set to -1. If there is a Unix error io_errno must be set to the errno value, and if there is a Win32 error, win32 and lerror must be set.

  Note: Bacula will call IO_SEEK only when writing a sparse file.

## bool checkFile(bpContext *ctx, char *fname)

If this entry point is set, Bacula will call it after backing up all file data during an Accurate backup. It will be passed the full filename for each file that Bacula is proposing to mark as deleted. Only files previously backed up but not backed up in the current session will be marked to be deleted. If you return false, the file will be be marked deleted. If you return true the file will not be marked deleted. This permits a plugin to ensure that previously saved virtual files or files controlled by your plugin that have not change (not backed up in the current job) are not marked to be deleted. This entry point will only be called during Accurate Incrmental and Differential backup jobs.