xattr_name_with_flags.3   [plain text]

.\"
.\" Copyright (c) 2013 Apple Computer, Inc.  All rights reserved.
.\"
.Dd December 21, 2016
.Dt XATTR_NAME_WITH_FLAGS 3
.Os
.Sh NAME
.Nm xattr_preserve_for_intent , xattr_name_with_flags , xattr_name_without_flags ,
.Nm xattr_flags_from_name , xattr_intent_with_flags
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In xattr_flags.h
.Ft int
.Fn xattr_preserve_for_intent "const char *" "xattr_operation_intent_t"
.Ft char *
.Fn xattr_name_with_flags "const char *" "xattr_flags_t"
.Ft char *
.Fn xattr_name_without_flags "const char *"
.Ft xattr_flags_t
.Fn xattr_flags_from_name "const char *"
.Ft int
.Fn xattr_intent_with_flags "xattr_operation_intent_t" "xattr_flags_t"
.Sh DESCRIPTION
These functions are used in conjunction with copying extended attributes from
one file to another.  Various types of copying (an "intent") check flags to
determine which is allowed or not.
.Pp
The
.Fn xattr_name_with_flags
function returns an extended attribute name with the appropriate flags encoded
as a string; the
.Fn xattr_name_without_flags
undoes this, giving the name of the extended attribute without the flags
encoding.  The slight inverse of that is
.Fn xattr_flags_from_name ,
which will return the flags encoded in a name.
.Pp
The values returned by
.Fn xattr_name_with_flags
and
.Fn xattr_name_without_flags
are allocated using
.Xr malloc 3 ,
and should be released by the caller, using
.Xr free 3 .
.Pp
These functions also have an internal table of pre-defined names, maintained
by the operating system.
.Pp
The function
.Fn xattr_intent_with_flags
will return 0 if the
.Ar flags
argument indicates it should not be preserved for the given
intent, or 1 if it should.
.Pp
The function
.Fn xattr_preserve_for_intent
combines the functions above, and will return zero if the
named extended attribute should be preserved during a copy for
the given intent.
.Sh INTENT
The type
.Dt xattr_operation_intent_t
is an integral type, which is used to indicate what the intent for the operation
is.  The following intent values are defined:
.Bl -tag -width XATTR_OPERATION_INTENT_SHARE
.It Dv XATTR_OPERATION_INTENT_COPY
Indicates that the intent is to simply copy from the source to the destination.
E.g., with cp.  Most extended attributes should generally be preserved in this
case.
.It Dv XATTR_OPERATION_INTENT_SAVE
Indicates that intent is to perform a save (perhaps as in a "safe save").
This differs from a copy in that the content may be changing; the destination
may be over-writing or replacing the source, and some extended attributes should
not be preserved during this process.
.It Dv XATTR_OPERATION_INTENT_SHARE
Indicates that the intent is to share, or export, the object.  For example,
saving as an attachment in an email message, or placing in a public folder.
Sensitive information should probably not be preserved in this case.
.It Dv XATTR_OPERATION_INTENT_SYNC
Indicates that the intent is to sync the object to a service like iCloud.
.El
.Sh FLAGS
Various flags are defined by the type
.Dt xattr_flags_t ;
the currently-defined values for this are
.Bl -tag -width XATTR_FLAG_CONTENT_DEPENDENT
.It Dv XATTR_FLAG_NO_EXPORT
This indicates that the extended attribute should not be exported, or shared.
This is used with
.Dv XATTR_OPERATION_INTENT_SHARE .
.It Dv XATTR_FLAG_CONTENT_DEPENDENT
This indicates that the extended attribute is tied to the contents of the
file (or vice versa), such that it should be re-created when the contents
are changed.  A checksum, for example, should not be copied, and would thus
be marked with this flag.
.It Dv XATTR_FLAG_NEVER_PRESERVE
This indicates that the extended attribute should never be copied from a
source object to a destination, no matter what the given intent is.
.It Dv XATTR_FLAG_SYNCABLE
This indicates that the extended attribute should be copied when the file
is synced on services like iCloud. Sync services tends to want the metadata
synced to be kept to a bare minimum, and may enforce additional restrictions
on the acceptable size and number of extended attributes.
.El
.Sh EXAMPLE
The following example is a simple function that, given an extended attribute
name and an operation intent, will return whether or not the extended attribute
should be copied.  (This essentially does what
.Fn xattr_preserve_for_intent
does.)
.Bd -literal -offset indent
int
ShouldCopyEA(const char *eaName, xattr_operation_intent_t intent)
{
	xattr_flags_t flags = xattr_flags_from_name(eaName);
	return xattr_intent_with_flags(intent, flags);
}
.Ed
.Sh HISTORY
These functions first appeared in Mac OS in 2013.