.TH libjio 3 "21/Feb/2004"
.SH NAME
libjio - A library for Journaled I/O
.SH SYNOPSIS
.nf
.B #include <libjio.h>
.BI "jfs_t *jopen(const char *" name ", int " flags ", int " mode ",
.BI " unsigned int " jflags ");"
.BI "ssize_t jread(jfs_t *" fs ", void *" buf ", size_t " count ");"
.BI "ssize_t jpread(jfs_t *" fs ", void *" buf ", size_t " count ","
.BI " off_t " offset ");"
.BI "ssize_t jreadv(jfs_t *" fs ", struct iovec *" vector ","
.BI " int " count ");"
.BI "ssize_t jwrite(jfs_t *" fs ", const void *" buf ", size_t " count ");"
.BI "ssize_t jpwrite(jfs_t *" fs ", const void *" buf ", size_t " count ","
.BI " off_t " offset ");"
.BI "ssize_t jwritev(jfs_t *" fs ", const struct iovec *" vector ","
.BI " int " count ");"
.BI "int jtruncate(jfs_t *" fs ", off_t " lenght ");"
.BI "off_t jlseek(jfs_t *" fs ", off_t " offset ", int " whence ");"
.BI "int jclose(jfs_t *" fs ");"
.BI "jtrans_t *jtrans_new(jfs_t *" fs ", unsigned int " flags ");"
.BI "int jtrans_commit(jtrans_t *" ts ");"
.BI "int jtrans_add_r(jtrans_t *" ts ", void *" buf ","
.BI " size_t " count ", off_t " offset ");"
.BI "int jtrans_add_w(jtrans_t *" ts ", const void *" buf ","
.BI " size_t " count ", off_t " offset ");"
.BI "int jtrans_rollback(jtrans_t *" ts ");"
.BI "void jtrans_free(jtrans_t *" ts ");"
.BI "int jsync(jfs_t *" fs ");"
.BI "int jfs_autosync_start(jfs_t *" fs ", time_t " max_sec ","
.BI " size_t " max_bytes ");"
.BI "int jfs_autosync_stop(jfs_t *" fs ");"
.BI "int jmove_journal(jfs_t *" fs ", const char *" newpath ");"
.BI "enum jfsck_return jfsck(const char *" name ", const char *" jdir ","
.BI " jfsck_result *" res ", unsigned int " flags ");"
.BR "struct jfsck_result" " {"
int total; /* total transactions files we looked at */
int invalid; /* invalid files in the journal directory */
int in_progress; /* transactions in progress */
int broken; /* transactions broken */
int rollbacked; /* transactions that were rollbacked */
...
};
.BR "enum jfsck_return" " {"
J_ESUCCESS = 0, /* Success */
J_ENOENT = -1, /* No such file or directory */
J_ENOJOURNAL = -2, /* No journal associated with the given file */
J_ENOMEM = -3, /* Not enough free memory */
J_ECLEANUP = -4, /* Error cleaning the journal directory */
J_EIO = -5, /* I/O error */
};
.SH DESCRIPTION
libjio is a library to do transaction-oriented journaled I/O. This manpage
describes its C API very briefly, further information can be found in the
documentation that comes along with the library itself, or on the web at
http://blitiri.com.ar/p/libjio.
Functions can be grouped in three different groups: the common functions, the
UNIX-alike API, and the basic functions. All return 0 upon successful
completion and < 0 upon failure, unless otherwise noted.
The common functions provide functionality common to the other two:
.BR jopen() " and " jclose()
to open and close files in order to use them with the library, and
.B jfsck()
to provide integrity checking.
The UNIX-alike API mimics the traditional UNIX API by providing similar
interfaces to
.BR read(2) ", " write(2) ,
and friends.
The basic functions consist of
.BR jtrans_new() ", " jtrans_add_r() ", " jtrans_add_w() ", "
.BR jtrans_commit() " and " jtrans_rollback() .
They provide a lower-level method for manipulating transactions.
.SS TYPES AND STRUCTURES
.I jfs_t
represents an open file, and
.I jtrans_t
represents a transaction. Both are meant to be treated as opaque types.
.B struct jfsck_result
holds the results of a
.B jfsck()
run. The fields are described in the synopsis section.
.SS COMMON FUNCTIONS
To open a file, you should use
.BR jopen() ,
which is just like the normal
.B open(2)
call but returns an opaque pointer.
To close a file, use
.BR jclose() .
They're exactly like the
.BR open(2) " and " close(2)
functions but use a
.I jfs_t
instead of a file descriptor; take a look at their manpages if you have any
doubts about how to use them.
.B jmove_journal()
can be used to move the journal directory to a new location. It can be called
only when nobody else is using the file. It is usually not used, except for
very special cases.
.B jfs_autosync_start()
can be used to start a thread which will automatically perform a
.B jsync()
after the given number of seconds or the given number of bytes written using
lingering transactions (whatever comes first). It's very useful when using
lingering transactions.
.B jfs_autosync_stop()
stops the thread started by
.BR jfs_autosync_start() .
The thread is also stopped automatically when
.B jclose()
is called.
.B jfsck()
takes as the first two parameters the path to the file to check and the path
to the journal directory (usually NULL for the default, unless you've changed
it manually using
.BR jmove_journal() ),
and optionally a flags parameter, which can be 0 for the default behaviour, or
J_CLEANUP to indicate that the journal should be cleaned up after successful
recovery.
It is used to perform journal checking and recovery in case of a crash. It
must be performed when nobody else is using the file (like in the case of a
filesystem which can't be mounted), and it returns 0 if success or an error
code != 0 in case of a failure. If it succeeded, it will fill jfsck_result
summarizing the outcome of the operation. The error codes can be either
.I J_ENOENT
(no such file),
.I J_ENOJOURNAL
(no journal associated with that file),
.I J_ENOMEM
(not enough free memory),
.I J_ECLEANUP
(error cleaning the journal directory), and
.I J_EIO
(I/O error). There is also a program named
.I jiofsck
which is just a simple human frontend to this function.
.SS UNIX-alike API
The UNIX-alike API, as explained before, consists of the functions
.BR jread() ", " jpread() ", " jreadv() ", " jwrite() ", " jpwrite() ", "
.BR jwritev() ", " jtruncate() "and " jlseek() .
They are all exactly like the UNIX equivalent, and behave the same way, with
the only exception that instead of a file descriptor you need to pass a
pointer to a
.IR "jfs_t" .
Again, I will not duplicate the manpage for all these functions, just refer to
the regular UNIX versions to see how to use them, they all have the same
semantics and behave the same way.
.SS BASIC FUNCTIONS
The basic functions are the ones which manipulate transactions directly:
.BR jtrans_new() ", " jtrans_add_r() ", " jtrans_add_w() ", "
.BR jtrans_commit() ", " jtrans_rollback() " and " jtrans_free()" .
These are intended to be use when your application requires direct control
over the transactions.
.BR jtrans_new() " and " jtrans_free()
just return a new
.I jtrans_t
and free a given one; the former should be called prior any use, and the
latter when you want to destroy a transaction. Note that
.B jtrans_free()
is not a disk operation, but only frees the pointers that were previously
allocated by the library; all disk operations are performed by the other two
functions.
You can add multiple read and write operations to a transaction, and they will
be applied in order.
.B jtrans_add_w()
is used to add write operations to a transaction, and it takes the same
parameters as
.BR pwrite() :
a buffer, its length and the offset where it should be applied, and adds it to
the transaction. The buffer is copied internally and can be free()d right
after this function returns.
.B jtrans_add_r()
is used to add read operations to a transaction, and it takes the same
parameters as
.BR pread() :
a buffer, its length and the offset where it should read from, and adds it to
the transaction. Note that if there is not enough data in the file to read
the specified amount of bytes, the commit will fail, so do not attempt to read
beyond EOF (you can use jread() for that purpose).
.B jtrans_commit()
commits the given transaction to disk. After it has returned, write operations
have been saved to the disk, and read operations have been read from it. The
commit operation is atomic with regards to other read or write operations on
different processes, as long as they all access it via libjio. It returns the
number 0 on success, -1 if there was an error but atomic warantees were
preserved, or -2 if there was an error and there is a possible break of atomic
warantees (which is an indication of a severe underlying condition).
.B jtrans_rollback()
reverses a transaction that was applied with
.BR jtrans_commit() ,
and leaves the file as it was before applying it. Be very very careful with
this function, it's quite dangerous if you don't know for sure that you're
doing the right thing. It returns the same values as
.BR jtrans_commit() .
.SH SEE ALSO
.BR open (2),
.BR read (2),
.BR write (2),
.BR readv (2),
.BR writev (2),
.BR pread (2),
.BR pwrite (2),
.BR ftruncate (2),
.BR lseek (2),
.BR close (2)
.SH BUGS
If you want to report bugs, or have any questions or comments, just let me
know at albertito@blitiri.com.ar.