376 lines
12 KiB
Groff
376 lines
12 KiB
Groff
.\" Copyright (c) 2003-2007 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 August 5, 2008
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.Dt ARCHIVE_WRITE_DISK 3
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.Os
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.Sh NAME
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.Nm archive_write_disk_new ,
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.Nm archive_write_disk_set_options ,
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.Nm archive_write_disk_set_skip_file ,
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.Nm archive_write_disk_set_group_lookup ,
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.Nm archive_write_disk_set_standard_lookup ,
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.Nm archive_write_disk_set_user_lookup ,
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.Nm archive_write_header ,
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.Nm archive_write_data ,
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.Nm archive_write_finish_entry ,
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.Nm archive_write_close ,
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.Nm archive_write_finish
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.Nd functions for creating objects on 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_write_disk_new "void"
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.Ft int
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.Fn archive_write_disk_set_options "struct archive *" "int flags"
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.Ft int
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.Fn archive_write_disk_set_skip_file "struct archive *" "dev_t" "ino_t"
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.Ft int
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.Fo archive_write_disk_set_group_lookup
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.Fa "struct archive *"
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.Fa "void *"
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.Fa "gid_t (*)(void *, const char *gname, gid_t gid)"
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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_write_disk_set_standard_lookup "struct archive *"
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.Ft int
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.Fo archive_write_disk_set_user_lookup
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.Fa "struct archive *"
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.Fa "void *"
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.Fa "uid_t (*)(void *, const char *uname, uid_t uid)"
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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_write_header "struct archive *" "struct archive_entry *"
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.Ft ssize_t
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.Fn archive_write_data "struct archive *" "const void *" "size_t"
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.Ft int
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.Fn archive_write_finish_entry "struct archive *"
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.Ft int
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.Fn archive_write_close "struct archive *"
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.Ft int
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.Fn archive_write_finish "struct archive *"
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.Sh DESCRIPTION
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These functions provide a complete API for creating objects on
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disk from
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.Tn struct archive_entry
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descriptions.
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They are most naturally used when extracting objects from an archive
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using the
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.Fn archive_read
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interface.
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The general process is to read
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.Tn struct archive_entry
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objects from an archive, then write those objects to a
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.Tn struct archive
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object created using the
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.Fn archive_write_disk
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family functions.
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This interface is deliberately very similar to the
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.Fn archive_write
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interface used to write objects to a streaming archive.
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.Bl -tag -width indent
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.It Fn archive_write_disk_new
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Allocates and initializes a
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.Tn struct archive
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object suitable for writing objects to disk.
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.It Fn archive_write_disk_set_skip_file
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Records the device and inode numbers of a file that should not be
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overwritten.
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This is typically used to ensure that an extraction process does not
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overwrite the archive from which objects are being read.
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This capability is technically unnecessary but can be a significant
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performance optimization in practice.
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.It Fn archive_write_disk_set_options
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The options field consists of a bitwise OR of one or more of the
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following values:
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.Bl -tag -compact -width "indent"
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.It Cm ARCHIVE_EXTRACT_OWNER
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The user and group IDs should be set on the restored file.
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By default, the user and group IDs are not restored.
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.It Cm ARCHIVE_EXTRACT_PERM
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Full permissions (including SGID, SUID, and sticky bits) should
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be restored exactly as specified, without obeying the
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current umask.
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Note that SUID and SGID bits can only be restored if the
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user and group ID of the object on disk are correct.
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If
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.Cm ARCHIVE_EXTRACT_OWNER
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is not specified, then SUID and SGID bits will only be restored
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if the default user and group IDs of newly-created objects on disk
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happen to match those specified in the archive entry.
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By default, only basic permissions are restored, and umask is obeyed.
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.It Cm ARCHIVE_EXTRACT_TIME
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The timestamps (mtime, ctime, and atime) should be restored.
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By default, they are ignored.
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Note that restoring of atime is not currently supported.
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.It Cm ARCHIVE_EXTRACT_NO_OVERWRITE
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Existing files on disk will not be overwritten.
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By default, existing regular files are truncated and overwritten;
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existing directories will have their permissions updated;
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other pre-existing objects are unlinked and recreated from scratch.
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.It Cm ARCHIVE_EXTRACT_UNLINK
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Existing files on disk will be unlinked before any attempt to
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create them.
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In some cases, this can prove to be a significant performance improvement.
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By default, existing files are truncated and rewritten, but
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the file is not recreated.
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In particular, the default behavior does not break existing hard links.
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.It Cm ARCHIVE_EXTRACT_ACL
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Attempt to restore ACLs.
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By default, extended ACLs are ignored.
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.It Cm ARCHIVE_EXTRACT_FFLAGS
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Attempt to restore extended file flags.
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By default, file flags are ignored.
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.It Cm ARCHIVE_EXTRACT_XATTR
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Attempt to restore POSIX.1e extended attributes.
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By default, they are ignored.
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.It Cm ARCHIVE_EXTRACT_SECURE_SYMLINKS
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Refuse to extract any object whose final location would be altered
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by a symlink on disk.
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This is intended to help guard against a variety of mischief
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caused by archives that (deliberately or otherwise) extract
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files outside of the current directory.
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The default is not to perform this check.
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If
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.Cm ARCHIVE_EXTRACT_UNLINK
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is specified together with this option, the library will
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remove any intermediate symlinks it finds and return an
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error only if such symlink could not be removed.
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.It Cm ARCHIVE_EXTRACT_SECURE_NODOTDOT
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Refuse to extract a path that contains a
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.Pa ..
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element anywhere within it.
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The default is to not refuse such paths.
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Note that paths ending in
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.Pa ..
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always cause an error, regardless of this flag.
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.It Cm ARCHIVE_EXTRACT_SPARSE
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Scan data for blocks of NUL bytes and try to recreate them with holes.
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This results in sparse files, independent of whether the archive format
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supports or uses them.
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.El
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.It Xo
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.Fn archive_write_disk_set_group_lookup ,
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.Fn archive_write_disk_set_user_lookup
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.Xc
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The
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.Tn struct archive_entry
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objects contain both names and ids that can be used to identify users
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and groups.
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These names and ids describe the ownership of the file itself and
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also appear in ACL lists.
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By default, the library uses the ids and ignores the names, but
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this can be overridden by registering user and group lookup functions.
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To register, you must provide a lookup function which
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accepts both a name and id and returns a suitable id.
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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.
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.It Fn archive_write_disk_set_standard_lookup
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This convenience function installs a standard set of user
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and group lookup functions.
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These functions use
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.Xr getpwnam 3
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and
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.Xr getgrnam 3
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to convert names to ids, defaulting to the ids 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 getpwnam 3
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and
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.Xr getgrnam 3 .
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.It Fn archive_write_header
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Build and write a header using the data in the provided
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.Tn struct archive_entry
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structure.
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See
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.Xr archive_entry 3
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for information on creating and populating
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.Tn struct archive_entry
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objects.
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.It Fn archive_write_data
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Write data corresponding to the header just written.
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Returns number of bytes written or -1 on error.
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.It Fn archive_write_finish_entry
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Close out the entry just written.
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Ordinarily, clients never need to call this, as it
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is called automatically by
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.Fn archive_write_next_header
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and
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.Fn archive_write_close
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as needed.
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.It Fn archive_write_close
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Set any attributes that could not be set during the initial restore.
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For example, directory timestamps are not restored initially because
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restoring a subsequent file would alter that timestamp.
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Similarly, non-writable directories are initially created with
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write permissions (so that their contents can be restored).
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The
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.Nm
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library maintains a list of all such deferred attributes and
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sets them when this function is invoked.
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.It Fn archive_write_finish
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Invokes
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.Fn archive_write_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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Many of these functions are also documented under
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.Xr archive_write 3 .
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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 non-zero
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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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.Fn archive_errno
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and
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.Fn archive_error_string
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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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.Pp
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.Fn archive_write_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.
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.Pp
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.Fn archive_write_data
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returns a count of the number of bytes actually written.
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On error, -1 is returned and the
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.Fn archive_errno
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and
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.Fn archive_error_string
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functions will return appropriate values.
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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 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_write_disk
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interface was added to
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.Nm libarchive 2.0
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and first appeared in
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.Fx 6.3 .
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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@acm.org .
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.Sh BUGS
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Directories are actually extracted in two distinct phases.
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Directories are created during
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.Fn archive_write_header ,
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but final permissions are not set until
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.Fn archive_write_close .
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This separation is necessary to correctly handle borderline
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cases such as a non-writable directory containing
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files, but can cause unexpected results.
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In particular, directory permissions are not fully
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restored until the archive is closed.
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If you use
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.Xr chdir 2
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to change the current directory between calls to
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.Fn archive_read_extract
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or before calling
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.Fn archive_read_close ,
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you may confuse the permission-setting logic with
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the result that directory permissions are restored
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incorrectly.
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.Pp
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The library attempts to create objects with filenames longer than
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.Cm PATH_MAX
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by creating prefixes of the full path and changing the current directory.
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Currently, this logic is limited in scope; the fixup pass does
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not work correctly for such objects and the symlink security check
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option disables the support for very long pathnames.
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.Pp
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Restoring the path
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.Pa aa/../bb
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does create each intermediate directory.
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In particular, the directory
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.Pa aa
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is created as well as the final object
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.Pa bb .
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In theory, this can be exploited to create an entire directory hierarchy
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with a single request.
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Of course, this does not work if the
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.Cm ARCHIVE_EXTRACT_NODOTDOT
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option is specified.
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.Pp
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Implicit directories are always created obeying the current umask.
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Explicit objects are created obeying the current umask unless
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.Cm ARCHIVE_EXTRACT_PERM
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is specified, in which case they current umask is ignored.
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.Pp
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SGID and SUID bits are restored only if the correct user and
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group could be set.
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If
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.Cm ARCHIVE_EXTRACT_OWNER
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is not specified, then no attempt is made to set the ownership.
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In this case, SGID and SUID bits are restored only if the
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user and group of the final object happen to match those specified
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in the entry.
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.Pp
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The
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.Dq standard
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user-id and group-id lookup functions are not the defaults because
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.Xr getgrnam 3
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and
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.Xr getpwnam 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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There should be a corresponding
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.Nm archive_read_disk
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interface that walks a directory hierarchy and returns archive
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entry objects.
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