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    SubjectRe: unlink(nonexistent): EROFS or ENOENT?
    Thank you for the answer.  I thought noone will reply... ;)

    06.06.2011 07:39, Ted Ts'o wrote:
    > On Sun, May 29, 2011 at 08:08:55PM +0400, Michael Tokarev wrote:
    >> Hello.
    >>
    >> Just noticed that at least on ext4, unlinking a
    >> non-existing file from a read-only filesystem
    >> results in EROFS instead of ENOENT. I'd expect
    >> it return ENOENT - it is more logical, at least
    >> in my opinion.
    >>
    >> For one, (readonly) NFS mount returns ENOENT in
    >> this case.
    >
    > Um, it doesn't for me. Testing on v3.0-rc1:
    >
    > # ls /test/foo; rm /test/foo
    > ls: cannot access /test/foo: No such file or directory
    > rm: cannot remove `/test/foo': No such file or directory

    This is a hack in coreutils rm to work around this
    kernel change. The comment at
    http://git.savannah.gnu.org/cgit/coreutils.git/tree/src/remove.c#n450
    says:

    /* The unlinkat from kernels like linux-2.6.32 reports EROFS even for
    nonexistent files. When the file is indeed missing, map that to ENOENT,
    so that rm -f ignores it, as required. Even without -f, this is useful
    because it makes rm print the more precise diagnostic. */

    so that rm(1) calls stat(2) to see if the file actually
    exist if unlinkat() returned EROFS, and turns this errno
    into ENOENT.

    That is, rm(1) output is not a good indicator. Use

    strace rm -f /test/foo 2>&1 | grep unlink

    to see the actual errno reported by the kernel.

    Here's the POSIX description of unlink (and unlinkat) again:
    http://pubs.opengroup.org/onlinepubs/009695399/functions/unlink.html

    Thanks!

    /mjt


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