tar_open






tar_open, tar_close − access a tar archive via a handle

#include<libtar.h> , char *int tar_open(TAR **t , int
tartype_t *type , int int mode

, int int tar_fdopen(TAR **t , tartype_t *char *pathname ,
int int oflags );int options

int tar_fd(TAR *t");"

int tar_close(TAR *t");"

This man page documents version 1.2 of libtar.

The tar_open() function opens a tar archive file
corresponding to the filename named by the pathname
argument.  The oflags argument must be either O_RDONLY or
O_WRONLY.

The type argument specifies the access methods for the given
file type.  The tartype_t structure has members named
openfunc, closefunc, readfunc() and writefunc(), which are
pointers to the functions for opening, closing, reading, and
writing the file, respectively.  If type is NULL, the file
type defaults to a normal file, and the standard open(),
close(), read(), and write() functions are used.

The options argument is a logical‐or’ed combination of zero
or more of the following:

TAR_GNU
     Use GNU extensions.

TAR_VERBOSE
     Send status messages to stdout.

TAR_NOOVERWRITE
     Do not overwrite pre‐existing files.

TAR_IGNORE_EOT
     Skip all‐zero blocks instead of treating them as EOT.

TAR_IGNORE_MAGIC
     Do not validate the magic field in file headers.

TAR_CHECK_VERSION
     Check the version field in file headers.  (This field
     is normally ignored.)

TAR_IGNORE_CRC
     Do not validate the CRC of file headers.


     The tar_open() function allocates memory for a TAR









                             ‐2‐


handle, and a pointer to the allocated memory is saved in
the location specified by t.  The TAR handle may be passed
to other libtar calls to modify the opened tar archive.  The
TAR handle maintains all of the information about the open
tar archive, including the archive type, options, and oflags
selected when tar_open() was called.

The TAR handle generated by tar_open() contains a file
header structure.  When reading a tar archive, this
structure contains the last file header read from the tar
archive.  When writing a tar archive, this structure is used
as a staging area to construct the next file header to be
written to the archive.  In addition, the TAR handle
contains a hash table which is used to keep track of the
device and inode information for each file which gets
written to the tar archive.  This is used to detect hard
links, so that files do not need to be duplicated in the
archive.

The tar_fdopen() function is identical to the tar_open()
function, except that fd is used as the previously‐opened
file descriptor for the tar file instead of calling
type‐>openfunc() to open the file.

The tar_fd() function returns the file descriptor associated
with the TAR handle t.

The tar_close() function closes the file descriptor
associated with the TAR handle t and frees all dynamically‐
allocated memory.

The tar_open(), tar_fdopen(), and tar_close() functions
return 0 on success.  On failure, they return −1 and set
errno.

The tar_fd() function returns the file descriptor associated
with the TAR handle t.

tar_open() will fail if:

EINVAL
     The oflags argument was something other than O_RDONLY
     or O_WRONLY.

     In addition, tar_open() and tar_close() may fail if it
cannot allocate memory using calloc(), or if the open or
close functions for the specified tar archive type fail.