ARCHIVE_READ_DISK(3)	 BSD Library Functions Manual	  ARCHIVE_READ_DISK(3)

NAME

     archive_read_disk_new, archive_read_disk_set_behavior,

     archive_read_disk_set_symlink_logical,

     archive_read_disk_set_symlink_physical,

     archive_read_disk_set_symlink_hybrid, archive_read_disk_entry_from_file,

     archive_read_disk_gname, archive_read_disk_uname,

     archive_read_disk_set_uname_lookup, archive_read_disk_set_gname_lookup,

     archive_read_disk_set_standard_lookup — functions for reading objects

     from disk

LIBRARY

     Streaming Archive Library (libarchive, -larchive)

SYNOPSIS

     #include <archive.h>

     struct archive *

     archive_read_disk_new(void);

     int

     archive_read_disk_set_behavior(struct archive *, int);

     int

     archive_read_disk_set_symlink_logical(struct archive *);

     int

     archive_read_disk_set_symlink_physical(struct archive *);

     int

     archive_read_disk_set_symlink_hybrid(struct archive *);

     const char *

     archive_read_disk_gname(struct archive *, gid_t);

     const char *

     archive_read_disk_uname(struct archive *, uid_t);

     int

     archive_read_disk_set_gname_lookup(struct archive *, void *,

	 const char *(*lookup)(void *, gid_t), void (*cleanup)(void *));

     int

     archive_read_disk_set_uname_lookup(struct archive *, void *,

	 const char *(*lookup)(void *, uid_t), void (*cleanup)(void *));

     int

     archive_read_disk_set_standard_lookup(struct archive *);

     int

     archive_read_disk_entry_from_file(struct archive *,

	 struct archive_entry *, int fd, const struct stat *);

DESCRIPTION

     These functions provide an API for reading information about objects on

     disk.  In particular, they provide an interface for populating struct

     archive_entry objects.

     archive_read_disk_new()

	     Allocates and initializes a struct archive object suitable for

	     reading object information from disk.

     archive_read_disk_set_behavior()

	     Configures various behavior options when reading entries from

	     disk.  The flags field consists of a bitwise OR of one or more of

	     the following values:

	     ARCHIVE_READDISK_HONOR_NODUMP

		     Skip files and directories with the nodump file attribute

		     (file flag) set.  By default, the nodump file atrribute

		     is ignored.

	     ARCHIVE_READDISK_MAC_COPYFILE

		     Mac OS X specific. Read metadata (ACLs and extended

		     attributes) with copyfile(3).  By default, metadata is

		     read using copyfile(3).

	     ARCHIVE_READDISK_NO_ACL

		     Do not read Access Control Lists.	By default, ACLs are

		     read from disk.

	     ARCHIVE_READDISK_NO_FFLAGS

		     Do not read file attributes (file flags).	By default,

		     file attributes are read from disk.  See chattr(1)

		     (Linux) or chflags(1) (FreeBSD, Mac OS X) for more infor‐

		     mation on file attributes.

	     ARCHIVE_READDISK_NO_TRAVERSE_MOUNTS

		     Do not traverse mount points.  By defaut, moint points

		     are traversed.

	     ARCHIVE_READDISK_NO_XATTR

		     Do not read extended file attributes (xattrs).  By

		     default, extended file attributes are read from disk.

		     See xattr(7) (Linux), xattr(2) (Mac OS X), or

		     getextattr(8) (FreeBSD) for more information on extended

		     file attributes.

	     ARCHIVE_READDISK_RESTORE_ATIME

		     Restore access time of traversed files.  By default,

		     access time of traversed files is not restored.

     archive_read_disk_set_symlink_logical(),

	     archive_read_disk_set_symlink_physical(),

	     archive_read_disk_set_symlink_hybrid()

	     This sets the mode used for handling symbolic links.  The

	     “logical” mode follows all symbolic links.  The “physical” mode

	     does not follow any symbolic links.  The “hybrid” mode currently

	     behaves identically to the “logical” mode.

     archive_read_disk_gname(), archive_read_disk_uname()

	     Returns a user or group name given a gid or uid value.  By

	     default, these always return a NULL string.

     archive_read_disk_set_gname_lookup(),

	     archive_read_disk_set_uname_lookup()

	     These allow you to override the functions used for user and group

	     name lookups.  You may also provide a void * pointer to a private

	     data structure and a cleanup function for that data.  The cleanup

	     function will be invoked when the struct archive object is

	     destroyed or when new lookup functions are registered.

     archive_read_disk_set_standard_lookup()

	     This convenience function installs a standard set of user and

	     group name lookup functions.  These functions use getpwuid(3) and

	     getgrgid(3) to convert ids to names, defaulting to NULL if the

	     names cannot be looked up.  These functions also implement a sim‐

	     ple memory cache to reduce the number of calls to getpwuid(3) and

	     getgrgid(3).

     archive_read_disk_entry_from_file()

	     Populates a struct archive_entry object with information about a

	     particular file.  The archive_entry object must have already been

	     created with archive_entry_new(3) and at least one of the source

	     path or path fields must already be set.  (If both are set, the

	     source path will be used.)

	     Information is read from disk using the path name from the struct

	     archive_entry object.  If a file descriptor is provided, some

	     information will be obtained using that file descriptor, on plat‐

	     forms that support the appropriate system calls.

	     If a pointer to a struct stat is provided, information from that

	     structure will be used instead of reading from the disk where

	     appropriate.  This can provide performance benefits in scenarios

	     where struct stat information has already been read from the disk

	     as a side effect of some other operation.	(For example, direc‐

	     tory traversal libraries often provide this information.)

	     Where necessary, user and group ids are converted to user and

	     group names using the currently registered lookup functions

	     above.  This affects the file ownership fields and ACL values in

	     the struct archive_entry object.

     More information about the struct archive object and the overall design

     of the library can be found in the libarchive(3) overview.

EXAMPLE

     The following illustrates basic usage of the library by showing how to

     use it to copy an item on disk into an archive.

	   void

	   file_to_archive(struct archive *a, const char *name)

	   {

	     char buff[8192];

	     size_t bytes_read;

	     struct archive *ard;

	     struct archive_entry *entry;

	     int fd;

	     ard = archive_read_disk_new();

	     archive_read_disk_set_standard_lookup(ard);

	     entry = archive_entry_new();

	     fd = open(name, O_RDONLY);

	     if (fd < 0)

		return;

	     archive_entry_copy_pathname(entry, name);

	     archive_read_disk_entry_from_file(ard, entry, fd, NULL);

	     archive_write_header(a, entry);

	     while ((bytes_read = read(fd, buff, sizeof(buff))) > 0)

	       archive_write_data(a, buff, bytes_read);

	     archive_write_finish_entry(a);

	     archive_read_free(ard);

	     archive_entry_free(entry);

	   }

RETURN VALUES

     Most functions return ARCHIVE_OK (zero) on success, or one of several

     negative error codes for errors.  Specific error codes include:

     ARCHIVE_RETRY for operations that might succeed if retried, ARCHIVE_WARN

     for unusual conditions that do not prevent further operations, and

     ARCHIVE_FATAL for serious errors that make remaining operations impossi‐

     ble.

     archive_read_disk_new() returns a pointer to a newly-allocated struct

     archive object or NULL if the allocation failed for any reason.

     archive_read_disk_gname() and archive_read_disk_uname() return const char

     * pointers to the textual name or NULL if the lookup failed for any rea‐

     son.  The returned pointer points to internal storage that may be reused

     on the next call to either of these functions; callers should copy the

     string if they need to continue accessing it.

ERRORS

     Detailed error codes and textual descriptions are available from the

     archive_errno() and archive_error_string() functions.

SEE ALSO

     archive_read(3), archive_util(3), archive_write(3),

     archive_write_disk(3), tar(1), libarchive(3)

HISTORY

     The libarchive library first appeared in FreeBSD 5.3.  The

     archive_read_disk interface was added to libarchive 2.6 and first

     appeared in FreeBSD 8.0.

AUTHORS

     The libarchive library was written by Tim Kientzle

     <kientzle@FreeBSD.org>.

BUGS

     The “standard” user name and group name lookup functions are not the

     defaults because getgrgid(3) and getpwuid(3) are sometimes too large for

     particular applications.  The current design allows the application

     author to use a more compact implementation when appropriate.

     The full list of metadata read from disk by

     archive_read_disk_entry_from_file() is necessarily system-dependent.

     The archive_read_disk_entry_from_file() function reads as much informa‐

     tion as it can from disk.	Some method should be provided to limit this

     so that clients who do not need ACLs, for instance, can avoid the extra

     work needed to look up such information.

     This API should provide a set of methods for walking a directory tree.

     That would make it a direct parallel of the archive_read(3) API.  When

     such methods are implemented, the “hybrid” symbolic link mode will make

     sense.

BSD				 April 3, 2017				   BSD