.\" Copyright (c) 2003-2009 Tim Kientzle

.\" All rights reserved.

.\"

.\" Redistribution and use in source and binary forms, with or without

.\" modification, are permitted provided that the following conditions

.\" are met:

.\" 1. Redistributions of source code must retain the above copyright

.\"    notice, this list of conditions and the following disclaimer.

.\" 2. Redistributions in binary form must reproduce the above copyright

.\"    notice, this list of conditions and the following disclaimer in the

.\"    documentation and/or other materials provided with the distribution.

.\"

.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND

.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE

.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

.\" SUCH DAMAGE.

.\"

.\" $FreeBSD$

.\"

.Dd April 3, 2017

.Dt ARCHIVE_READ_DISK 3

.Os

.Sh NAME

.Nm archive_read_disk_new ,

.Nm archive_read_disk_set_behavior ,

.Nm archive_read_disk_set_symlink_logical ,

.Nm archive_read_disk_set_symlink_physical ,

.Nm archive_read_disk_set_symlink_hybrid ,

.Nm archive_read_disk_entry_from_file ,

.Nm archive_read_disk_gname ,

.Nm archive_read_disk_uname ,

.Nm archive_read_disk_set_uname_lookup ,

.Nm archive_read_disk_set_gname_lookup ,

.Nm archive_read_disk_set_standard_lookup

.Nd functions for reading objects from disk

.Sh LIBRARY

Streaming Archive Library (libarchive, -larchive)

.Sh SYNOPSIS

.In archive.h

.Ft struct archive *

.Fn archive_read_disk_new "void"

.Ft int

.Fn archive_read_disk_set_behavior "struct archive *" "int"

.Ft int

.Fn archive_read_disk_set_symlink_logical "struct archive *"

.Ft int

.Fn archive_read_disk_set_symlink_physical "struct archive *"

.Ft int

.Fn archive_read_disk_set_symlink_hybrid "struct archive *"

.Ft const char *

.Fn archive_read_disk_gname "struct archive *" "gid_t"

.Ft const char *

.Fn archive_read_disk_uname "struct archive *" "uid_t"

.Ft int

.Fo archive_read_disk_set_gname_lookup

.Fa "struct archive *"

.Fa "void *"

.Fa "const char *(*lookup)(void *, gid_t)"

.Fa "void (*cleanup)(void *)"

.Fc

.Ft int

.Fo archive_read_disk_set_uname_lookup

.Fa "struct archive *"

.Fa "void *"

.Fa "const char *(*lookup)(void *, uid_t)"

.Fa "void (*cleanup)(void *)"

.Fc

.Ft int

.Fn archive_read_disk_set_standard_lookup "struct archive *"

.Ft int

.Fo archive_read_disk_entry_from_file

.Fa "struct archive *"

.Fa "struct archive_entry *"

.Fa "int fd"

.Fa "const struct stat *"

.Fc

.Sh DESCRIPTION

These functions provide an API for reading information about

objects on disk.

In particular, they provide an interface for populating

.Tn struct archive_entry

objects.

.Bl -tag -width indent

.It Fn archive_read_disk_new

Allocates and initializes a

.Tn struct archive

object suitable for reading object information from disk.

.It Fn 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:

.Bl -tag -compact -width "indent"

.It Cm ARCHIVE_READDISK_HONOR_NODUMP

Skip files and directories with the nodump file attribute (file flag) set.

By default, the nodump file atrribute is ignored.

.It Cm ARCHIVE_READDISK_MAC_COPYFILE

Mac OS X specific. Read metadata (ACLs and extended attributes) with

.Xr copyfile 3 .

By default, metadata is read using

.Xr copyfile 3 .

.It Cm ARCHIVE_READDISK_NO_ACL

Do not read Access Control Lists.

By default, ACLs are read from disk.

.It Cm ARCHIVE_READDISK_NO_FFLAGS

Do not read file attributes (file flags).

By default, file attributes are read from disk.

See

.Xr chattr 1

.Pq Linux

or

.Xr chflags 1

.Pq FreeBSD, Mac OS X

for more information on file attributes.

.It Cm ARCHIVE_READDISK_NO_TRAVERSE_MOUNTS

Do not traverse mount points.

By defaut, moint points are traversed.

.It Cm ARCHIVE_READDISK_NO_XATTR

Do not read extended file attributes (xattrs).

By default, extended file attributes are read from disk.

See

.Xr xattr 7

.Pq Linux ,

.Xr xattr 2

.Pq Mac OS X ,

or

.Xr getextattr 8

.Pq FreeBSD

for more information on extended file attributes.

.It Cm ARCHIVE_READDISK_RESTORE_ATIME

Restore access time of traversed files.

By default, access time of traversed files is not restored.

.El

.It Xo

.Fn archive_read_disk_set_symlink_logical ,

.Fn archive_read_disk_set_symlink_physical ,

.Fn archive_read_disk_set_symlink_hybrid

.Xc

This sets the mode used for handling symbolic links.

The

.Dq logical

mode follows all symbolic links.

The

.Dq physical

mode does not follow any symbolic links.

The

.Dq hybrid

mode currently behaves identically to the

.Dq logical

mode.

.It Xo

.Fn archive_read_disk_gname ,

.Fn archive_read_disk_uname

.Xc

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

By default, these always return a NULL string.

.It Xo

.Fn archive_read_disk_set_gname_lookup ,

.Fn archive_read_disk_set_uname_lookup

.Xc

These allow you to override the functions used for

user and group name lookups.

You may also provide a

.Tn void *

pointer to a private data structure and a cleanup function for

that data.

The cleanup function will be invoked when the

.Tn struct archive

object is destroyed or when new lookup functions are registered.

.It Fn archive_read_disk_set_standard_lookup

This convenience function installs a standard set of user

and group name lookup functions.

These functions use

.Xr getpwuid 3

and

.Xr getgrgid 3

to convert ids to names, defaulting to NULL if the names cannot

be looked up.

These functions also implement a simple memory cache to reduce

the number of calls to

.Xr getpwuid 3

and

.Xr getgrgid 3 .

.It Fn archive_read_disk_entry_from_file

Populates a

.Tn struct archive_entry

object with information about a particular file.

The

.Tn archive_entry

object must have already been created with

.Xr 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.)

.Pp

Information is read from disk using the path name from the

.Tn struct archive_entry

object.

If a file descriptor is provided, some information will be obtained using

that file descriptor, on platforms that support the appropriate

system calls.

.Pp

If a pointer to a

.Tn 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

.Tn struct stat

information has already been read from the disk as a side effect

of some other operation.

(For example, directory traversal libraries often provide this information.)

.Pp

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

.Tn struct archive_entry

object.

.El

More information about the

.Va struct archive

object and the overall design of the library can be found in the

.Xr libarchive 3

overview.

.Sh EXAMPLE

The following illustrates basic usage of the library by

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

.Bd -literal -offset indent

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);

}

.Ed

.Sh RETURN VALUES

Most functions return

.Cm ARCHIVE_OK

(zero) on success, or one of several negative

error codes for errors.

Specific error codes include:

.Cm ARCHIVE_RETRY

for operations that might succeed if retried,

.Cm ARCHIVE_WARN

for unusual conditions that do not prevent further operations, and

.Cm ARCHIVE_FATAL

for serious errors that make remaining operations impossible.

.Pp

.Fn archive_read_disk_new

returns a pointer to a newly-allocated

.Tn struct archive

object or NULL if the allocation failed for any reason.

.Pp

.Fn archive_read_disk_gname

and

.Fn archive_read_disk_uname

return

.Tn const char *

pointers to the textual name or NULL if the lookup failed for any reason.

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.

.\"

.Sh ERRORS

Detailed error codes and textual descriptions are available from the

.Fn archive_errno

and

.Fn archive_error_string

functions.

.\"

.Sh SEE ALSO

.Xr archive_read 3 ,

.Xr archive_util 3 ,

.Xr archive_write 3 ,

.Xr archive_write_disk 3 ,

.Xr tar 1 ,

.Xr libarchive 3

.Sh HISTORY

The

.Nm libarchive

library first appeared in

.Fx 5.3 .

The

.Nm archive_read_disk

interface was added to

.Nm libarchive 2.6

and first appeared in

.Fx 8.0 .

.Sh AUTHORS

.An -nosplit

The

.Nm libarchive

library was written by

.An Tim Kientzle Aq kientzle@FreeBSD.org .

.Sh BUGS

The

.Dq standard

user name and group name lookup functions are not the defaults because

.Xr getgrgid 3

and

.Xr getpwuid 3

are sometimes too large for particular applications.

The current design allows the application author to use a more

compact implementation when appropriate.

.Pp

The full list of metadata read from disk by

.Fn archive_read_disk_entry_from_file

is necessarily system-dependent.

.Pp

The

.Fn archive_read_disk_entry_from_file

function reads as much information 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.

.Pp

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

That would make it a direct parallel of the

.Xr archive_read 3

API.

When such methods are implemented, the

.Dq hybrid

symbolic link mode will make sense.