On 2015-12-21 20:32, Kai Krakow wrote:
Am Fri, 18 Dec 2015 03:01:06 +0100
schrieb Christoph Anton Mitterer <calestyo@xxxxxxxxxxxx>:
The manpage says:
ro Mount the filesystem read-only.
rw Mount the filesystem read-write.
That means: the filesystem... Not the block device...
No, that means: That particular instantiation of the VFS layer to access
the filesystem.
Not the filesystem (the filesystem is the data and metadata on disk),
not the block device (which is an abstraction used as a container for
the filesystem).
Sorry, it's kinda nitpicking. But actually, the file system IS
read-only: You cannot modify files from user's view.
From a non technical view point, yes, that is correct; until you have
undetected corruption in the journal or log or whatever other structure
is used for consistency, at which point it isn't read-only because the
filesystem just changed by virtue of you mounting it (and even without
that type of corruption, stuff gets changed on a 'read-only' mount
regardless in many filesystems, many of them track when the filesystem
was last mounted, how many times it's been mounted, and other similar
things).
What you actually want is not modifying the underlying storage which is
the block device and includes stuff like meta and journal data (which
is only indirectly visible to users at best).
No, the metadata and journal are a integral part of the filesystem
itself. Without those, there is no filesystem. That and the metadata
_is_ directly visible to the user, in the form of directory structure,
stat(), output from lsattr, and even stuff like FIEMAP and filefrag.
The filesystem _is_ the data and metadata on disk, as such, the
filesystem being read-only means that none of that data or metadata
should change.
You can argue that man pages are not particularly end-user friendly.
But for an admin this makes sense without being an fs developer.
That really depends. I'm not a FS developer, but I still expect when I
see 'read-only' that it means the same as 'immutable for everything
managed by that particular object that has been made read-only, for all
access methods through that object'. And while I bet most
administrators wouldn't use quite the same terminology, I would be
willing to bet that many of them have essentially the same expectation
unless specifically told otherwise on a case-by-case basis.
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