309 lines
9.1 KiB
Groff
309 lines
9.1 KiB
Groff
.\" Copyright (c) 2003-2009 Tim Kientzle
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd March 10, 2009
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.Dt ARCHIVE_READ_DISK 3
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.Os
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.Sh NAME
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.Nm archive_read_disk_new ,
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.Nm archive_read_disk_set_symlink_logical ,
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.Nm archive_read_disk_set_symlink_physical ,
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.Nm archive_read_disk_set_symlink_hybrid ,
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.Nm archive_read_disk_entry_from_file ,
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.Nm archive_read_disk_gname ,
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.Nm archive_read_disk_uname ,
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.Nm archive_read_disk_set_uname_lookup ,
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.Nm archive_read_disk_set_gname_lookup ,
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.Nm archive_read_disk_set_standard_lookup ,
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.Nm archive_read_close ,
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.Nm archive_read_free
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.Nd functions for reading objects from disk
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.Sh SYNOPSIS
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.In archive.h
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.Ft struct archive *
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.Fn archive_read_disk_new "void"
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.Ft int
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.Fn archive_read_disk_set_symlink_logical "struct archive *"
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.Ft int
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.Fn archive_read_disk_set_symlink_physical "struct archive *"
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.Ft int
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.Fn archive_read_disk_set_symlink_hybrid "struct archive *"
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.Ft int
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.Fn archive_read_disk_gname "struct archive *" "gid_t"
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.Ft int
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.Fn archive_read_disk_uname "struct archive *" "uid_t"
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.Ft int
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.Fo archive_read_disk_set_gname_lookup
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.Fa "struct archive *"
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.Fa "void *"
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.Fa "const char *(*lookup)(void *, gid_t)"
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.Fa "void (*cleanup)(void *)"
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.Fc
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.Ft int
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.Fo archive_read_disk_set_uname_lookup
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.Fa "struct archive *"
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.Fa "void *"
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.Fa "const char *(*lookup)(void *, uid_t)"
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.Fa "void (*cleanup)(void *)"
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.Fc
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.Ft int
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.Fn archive_read_disk_set_standard_lookup "struct archive *"
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.Ft int
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.Fo archive_read_disk_entry_from_file
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.Fa "struct archive *"
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.Fa "struct archive_entry *"
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.Fa "int fd"
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.Fa "const struct stat *"
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.Fc
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.Ft int
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.Fn archive_read_close "struct archive *"
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.Ft int
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.Fn archive_read_free "struct archive *"
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.Sh DESCRIPTION
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These functions provide an API for reading information about
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objects on disk.
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In particular, they provide an interface for populating
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.Tn struct archive_entry
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objects.
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.Bl -tag -width indent
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.It Fn archive_read_disk_new
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Allocates and initializes a
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.Tn struct archive
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object suitable for reading object information from disk.
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.It Xo
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.Fn archive_read_disk_set_symlink_logical ,
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.Fn archive_read_disk_set_symlink_physical ,
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.Fn archive_read_disk_set_symlink_hybrid
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.Xc
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This sets the mode used for handling symbolic links.
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The
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.Dq logical
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mode follows all symbolic links.
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The
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.Dq physical
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mode does not follow any symbolic links.
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The
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.Dq hybrid
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mode currently behaves identically to the
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.Dq logical
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mode.
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.It Xo
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.Fn archive_read_disk_gname ,
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.Fn archive_read_disk_uname
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.Xc
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Returns a user or group name given a gid or uid value.
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By default, these always return a NULL string.
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.It Xo
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.Fn archive_read_disk_set_gname_lookup ,
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.Fn archive_read_disk_set_uname_lookup
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.Xc
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These allow you to override the functions used for
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user and group name lookups.
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You may also provide a
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.Tn void *
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pointer to a private data structure and a cleanup function for
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that data.
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The cleanup function will be invoked when the
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.Tn struct archive
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object is destroyed or when new lookup functions are registered.
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.It Fn archive_read_disk_set_standard_lookup
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This convenience function installs a standard set of user
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and group name lookup functions.
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These functions use
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.Xr getpwuid 3
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and
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.Xr getgrgid 3
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to convert ids to names, defaulting to NULL if the names cannot
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be looked up.
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These functions also implement a simple memory cache to reduce
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the number of calls to
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.Xr getpwuid 3
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and
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.Xr getgrgid 3 .
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.It Fn archive_read_disk_entry_from_file
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Populates a
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.Tn struct archive_entry
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object with information about a particular file.
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The
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.Tn archive_entry
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object must have already been created with
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.Xr archive_entry_new 3
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and at least one of the source path or path fields must already be set.
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(If both are set, the source path will be used.)
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.Pp
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Information is read from disk using the path name from the
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.Tn struct archive_entry
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object.
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If a file descriptor is provided, some information will be obtained using
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that file descriptor, on platforms that support the appropriate
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system calls.
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.Pp
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If a pointer to a
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.Tn struct stat
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is provided, information from that structure will be used instead
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of reading from the disk where appropriate.
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This can provide performance benefits in scenarios where
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.Tn struct stat
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information has already been read from the disk as a side effect
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of some other operation.
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(For example, directory traversal libraries often provide this information.)
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.Pp
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Where necessary, user and group ids are converted to user and group names
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using the currently registered lookup functions above.
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This affects the file ownership fields and ACL values in the
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.Tn struct archive_entry
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object.
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.It Fn archive_read_close
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This currently does nothing.
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.It Fn archive_read_free
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Invokes
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.Fn archive_read_close
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if it was not invoked manually, then releases all resources.
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.El
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More information about the
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.Va struct archive
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object and the overall design of the library can be found in the
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.Xr libarchive 3
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overview.
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.Sh EXAMPLE
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The following illustrates basic usage of the library by
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showing how to use it to copy an item on disk into an archive.
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.Bd -literal -offset indent
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void
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file_to_archive(struct archive *a, const char *name)
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{
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char buff[8192];
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size_t bytes_read;
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struct archive *ard;
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struct archive_entry *entry;
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int fd;
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ard = archive_read_disk_new();
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archive_read_disk_set_standard_lookup(ard);
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entry = archive_entry_new();
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fd = open(name, O_RDONLY);
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if (fd < 0)
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return;
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archive_entry_copy_sourcepath(entry, name);
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archive_read_disk_entry_from_file(ard, entry, fd, NULL);
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archive_write_header(a, entry);
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while ((bytes_read = read(fd, buff, sizeof(buff))) > 0)
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archive_write_data(a, buff, bytes_read);
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archive_write_finish_entry(a);
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archive_read_free(ard);
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archive_entry_free(entry);
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}
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.Ed
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.Sh RETURN VALUES
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Most functions return
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.Cm ARCHIVE_OK
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(zero) on success, or one of several negative
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error codes for errors.
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Specific error codes include:
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.Cm ARCHIVE_RETRY
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for operations that might succeed if retried,
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.Cm ARCHIVE_WARN
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for unusual conditions that do not prevent further operations, and
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.Cm ARCHIVE_FATAL
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for serious errors that make remaining operations impossible.
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The
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.Xr archive_errno 3
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and
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.Xr archive_error_string 3
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functions can be used to retrieve an appropriate error code and a
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textual error message.
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(See
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.Xr archive_util 3
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for details.)
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.Pp
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.Fn archive_read_disk_new
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returns a pointer to a newly-allocated
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.Tn struct archive
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object or NULL if the allocation failed for any reason.
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.Pp
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.Fn archive_read_disk_gname
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and
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.Fn archive_read_disk_uname
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return
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.Tn const char *
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pointers to the textual name or NULL if the lookup failed for any reason.
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The returned pointer points to internal storage that
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may be reused on the next call to either of these functions;
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callers should copy the string if they need to continue accessing it.
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.Pp
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.Sh SEE ALSO
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.Xr archive_read 3 ,
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.Xr archive_write 3 ,
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.Xr archive_write_disk 3 ,
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.Xr tar 1 ,
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.Xr libarchive 3
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.Sh HISTORY
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The
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.Nm libarchive
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library first appeared in
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.Fx 5.3 .
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The
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.Nm archive_read_disk
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interface was added to
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.Nm libarchive 2.6
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and first appeared in
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.Fx 8.0 .
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm libarchive
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library was written by
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.An Tim Kientzle Aq kientzle@FreeBSD.org .
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.Sh BUGS
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The
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.Dq standard
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user name and group name lookup functions are not the defaults because
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.Xr getgrgid 3
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and
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.Xr getpwuid 3
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are sometimes too large for particular applications.
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The current design allows the application author to use a more
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compact implementation when appropriate.
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.Pp
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The full list of metadata read from disk by
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.Fn archive_read_disk_entry_from_file
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is necessarily system-dependent.
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.Pp
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The
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.Fn archive_read_disk_entry_from_file
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function reads as much information as it can from disk.
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Some method should be provided to limit this so that clients who
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do not need ACLs, for instance, can avoid the extra work needed
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to look up such information.
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.Pp
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This API should provide a set of methods for walking a directory tree.
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That would make it a direct parallel of the
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.Xr archive_read 3
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API.
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When such methods are implemented, the
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.Dq hybrid
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symbolic link mode will make sense.
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