[PATCH] manual: Correct argument order in mount examples (bug 27207)

[John McCabe]

Thank you for that; that's a fair point.

For what it's worth, I suspect it actually invalidates the first mount 
command in the examples in the patch; while the filesystemtype is 
ignored when MS_REMOUNT is specified, it isn't ignored for MS_RDONLY and 
MS_NOSUID, so I suspect something like the attached update would be more 
appropriate (done using an "amend last commit";  would I be better to 
re-do the thing?)

As for your additional observations, I'm happy for them to be dealt with 
separately :-)

John

------ Original Message ------
From: "DJ Delorie" <dj@redhat.com>
To: "John McCabe" <john@mccabe.org.uk>
Cc: libc-alpha@sourceware.org
Sent: 22/01/2021 18:09:29
Subject: Re: [PATCH] manual: Correct argument order in mount examples 
(bug 27207)

>"John McCabe" <john@mccabe.org.uk> writes:
>>   #include <sys/mount.h>
>>
>>  -mount("/dev/hdb", "/cdrom", MS_MGC_VAL | MS_RDONLY | MS_NOSUID, "");
>>  +mount("/dev/hdb", "/cdrom", "", MS_MGC_VAL | MS_RDONLY | MS_NOSUID, NULL);
>>
>>  -mount("/dev/hda2", "/mnt", MS_MGC_VAL | MS_REMOUNT, "");
>>  +mount("/dev/hda2", "/mnt", "", MS_MGC_VAL | MS_REMOUNT, NULL);
>>
>
>The mount(2) man page says the last argument is:
>
>        The data argument is interpreted by the different file systems.
>        Typically it is a string of comma-separated options understood by
>        this file system.  See mount(8) for details of the options
>        available for each filesystem type.
>
>and also says:
>
>        EFAULT One of the pointer arguments points outside the user
>               address space.
>
>Based on that, I think the original "" is correct (or at least safer ;)
>and that the manual was just missing the fstype argument.  I would be OK
>with this patch, with that change.
>
>But while we're here...
>
>Also, I will point out that the options we pass are obsolete, and some
>won't work in a post-2.4 world:
>
>        The mountflags argument may have the magic number 0xC0ED
>        (MS_MGC_VAL) in the top 16 bits (this was required in kernel
>        versions prior to 2.4, but is no longer required and ignored if
>        specified), and various mount flags in the low order 16 bits:
>
>        MS_REMOUNT
>               The following mountflags can be changed: MS_RDONLY,
>               MS_SYNCHRONOUS, MS_MANDLOCK; before kernel 2.6.16, the
>               following could also be changed: MS_NOATIME and
>               MS_NODIRATIME; and, additionally, before kernel 2.4.10,
>               the following could also be changed: MS_NOSUID, MS_NODEV,
>               MS_NOEXEC.
>
>That last paragraph is confusing; does it mean that ONLY before those
>versions, or SINCE before those versions?
>
>So we have an opportunity to update this part of our documentation, but
>I won't hold back the bugfix for it.
>
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