pthread_setname_np.3: EXAMPLES: remove a bug by simplify the code

From an email conversation with Alexis:

Hello Alexis,

On 8/6/21 7:06 PM, Alexis Wilke wrote:
> Hi guys,
>
> The pthread_setname_np(3) manual page has an example where the second
> argument is used to get a size of the thread name.
>
> https://man7.org/linux/man-pages/man3/pthread_setname_np.3.html#EXAMPLES
>
> The current code:
>
>            rc = pthread_getname_np(thread, thread_name,
>                                    (argc > 2) ? atoi(argv[1]) : NAMELEN);
>
> The suggested code:
>
>            rc = pthread_getname_np(thread, thread_name,
>                                    (argc > 2) ? atoi(argv[2]) : NAMELEN);

I agree that there's a problem, but I think we could go even simpler:

     rc = pthread_getname_np(thread, thread_name, NAMELEN);

> I'm thinking that maybe the author meant to compute the length like so:
>
>            rc = pthread_getname_np(thread, thread_name,
>                                    (argc > 2) ? strlen(argv[1]) + 1 :
> NAMELEN);
>
> But I think that the atoi() points to using argv[2] as a number
> representing the length.
>
> (Of course, it should be tested against NAMELEN as a maximum, but I
> understand that examples do not always show how to verify each possible
> error).

I imagine that the author's intention was to allow the user to do
experiments where argv[2] specified a number less than NAMELEN,
in order to see the resulting ERANGE error. But, that experiment
is of limited value, and complicates the code unnecessarily, IMO,
so that's why I made the change above.

--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

Reported-by: Alexis Wilke <alexis@m2osw.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/mount_setattr.2

@@ -270,8 +270,11 @@ and is implied by the noatime setting.
 All other access-time settings are mutually exclusive.
 .TP
 .BR MOUNT_ATTR__ATIME " - changing access-time settings"
-In the new mount API, the access-time values are an enum starting from 0.
-Even though they are an enum (in contrast to the other mount flags such as
+The access-time values listed below are an enumeration that
+includes the value zero, expressed in the bits defined by the mask
+.BR MOUNT_ATTR__ATIME .
+Even though these bits are an enumeration
+(in contrast to the other mount flags such as
 .BR MOUNT_ATTR_NOEXEC ),
 they are nonetheless passed in
 .I attr_set
@@ -282,12 +285,11 @@ for consistency with
 which introduced this behavior.
 .IP
 Note that,
-since access times are an enum
-not a bit map,
-users wanting to transition to a different access-time setting cannot simply
-specify the access-time setting in
-.I attr_set
-but must also set
+since the access-time values are an enumeration rather than bit values,
+a caller wanting to transition to a different access-time setting
+cannot simply specify the access-time setting in
+.IR attr_set ,
+but must also include
 .B MOUNT_ATTR__ATIME
 in the
 .I attr_clr
@@ -295,8 +297,10 @@ field.
 The kernel will verify that
 .B MOUNT_ATTR__ATIME
 isn't partially set in
-.IR attr_clr ,
-and that
+.IR attr_clr
+(i.e., either all bits in the
+.B MOUNT_ATTR__ATIME
+bit field are either set or clear), and that
 .I attr_set
 doesn't have any access-time bits set if
 .B MOUNT_ATTR__ATIME
@@ -368,42 +372,23 @@ For further details, see the subsection "ID-mapped mounts" under NOTES.
 The
 .I propagation
 field is used to specify the propagation type of the mount or mount tree.
-Mount propagation options are mutually exclusive;
-that is,
-the propagation values behave like an enum.
-The supported mount propagation types are:
+This field either has the value zero,
+meaning leave the propagation type unchanged, or it has one of
+the following values:
 .TP
 .B MS_PRIVATE
 Turn all mounts into private mounts.
-Mount and unmount events do not propagate into or out of this mount point.
 .TP
 .B MS_SHARED
 Turn all mounts into shared mounts.
-Mount points share events with members of a peer group.
-Mount and unmount events immediately under this mount point
-will propagate to the other mount points that are members of the peer group.
-Propagation here means that the same mount or unmount will automatically occur
-under all of the other mount points in the peer group.
-Conversely,
-mount and unmount events that take place under peer mount points
-will propagate to this mount point.
 .TP
 .B MS_SLAVE
 Turn all mounts into dependent mounts.
-Mount and unmount events propagate into this mount point
-from a shared peer group.
-Mount and unmount events under this mount point do not propagate to any peer.
 .TP
 .B MS_UNBINDABLE
-This is like a private mount,
-and in addition this mount can't be bind mounted.
-Attempts to bind mount this mount will fail.
-When a recursive bind mount is performed on a directory subtree,
-any bind mounts within the subtree are automatically pruned
-(i.e., not replicated)
-when replicating that subtree to produce the target subtree.
+Turn all mounts into unbindable mounts.
 .PP
-For further details on propagation types, see
+For further details on the above propagation types, see
 .BR mount_namespaces (7).
 .SH RETURN VALUE
 On success,

man3/pthread_setname_np.3

@@ -201,8 +201,7 @@ main(int argc, char *argv[])
 
     sleep(2);
 
-    rc = pthread_getname_np(thread, thread_name,
-                            (argc > 2) ? atoi(argv[1]) : NAMELEN);
+    rc = pthread_getname_np(thread, thread_name, NAMELEN);
     if (rc != 0)
         errExitEN(rc, "pthread_getname_np");
     printf("The thread name after setting it is %s.\en", thread_name);