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open(2): describe *at behavior for dirfd opened without O_SEARCH

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and move the BUGS paragraph about dirfd permissions into STANDARDS
section, noting that we provide POSIX-mandated implementation.

Reviewed by:	emaste, kevans
Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Differential revision:	https://reviews.freebsd.org/D43652
This commit is contained in:
Konstantin Belousov 2024-01-29 19:54:32 +02:00
parent c46860dbcb
commit a570fe4d0d
1 changed files with 24 additions and 12 deletions
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36
lib/libc/sys/open.2
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@ -25,7 +25,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd May 29, 2023
.Dd January 29, 2024
.Dt OPEN 2
.Os
.Sh NAME
@ -314,6 +314,12 @@ may not be used for any read operations like
The primary use for this descriptor will be as the lookup descriptor for the
.Fn *at
family of functions.
If
.Dv O_SEARCH
was not requested at open time, then the
.Fn *at
functions use the current directory permissions for the directory referenced
by the descriptor at the time of the call.
.Pp
.Dv O_PATH
returns a file descriptor that can be used as a directory file descriptor for
@ -661,6 +667,23 @@ when
is set in flags and the final component of pathname is a symbolic link
to distinguish it from the case of too many symbolic link traversals
in one of its non-final components.
.Pp
The Open Group Extended API Set 2 specification, that introduced the
.Fn *at
API, required that the test for whether
.Fa fd
is searchable is based on whether
.Fa fd
is open for searching, not whether the underlying directory currently
permits searches.
The present implementation of the
.Fa openat
system call is believed to be compatible with
.St -p1003.1-2017 ,
which specifies that behavior for
.Dv O_SEARCH ,
in the absence of the flag the implementation checks the current
permissions of a directory.
.Sh HISTORY
The
.Fn open
@ -673,17 +696,6 @@ function was introduced in
.Dv O_DSYNC
appeared in 13.0.
.Sh BUGS
The Open Group Extended API Set 2 specification requires that the test
for whether
.Fa fd
is searchable is based on whether
.Fa fd
is open for searching, not whether the underlying directory currently
permits searches.
The present implementation of the
.Fa openat
checks the current permissions of directory instead.
.Pp
The
.Fa mode
argument is variadic and may result in different calling conventions