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    Subject[patch] Re: [patch-2.4.0-test12-pre6] truncate(2) permissions
    On Wed, 6 Dec 2000, Alexander Viro wrote:
    > On Wed, 6 Dec 2000, Linus Torvalds wrote:
    > > Why remove the EROFS test?
    >
    > there, so if it's not a regular file we die before the call of permission(),
    > if it is and fs is readonly - we get -EROFS from permission() and die
    > there. In either case we don't get to the IS_RDONLY() check...

    just to add that I removed the immutable test for almost the same reason:

    a) we don't hit that test because permission takes care of it (for
    regulars/dirs/symlinks but here only regulars are important)

    b) the error returned by permission EACCES makes a lot more sense than
    EPERM we were trying to return. I already quotes Single UNIX v2 to explain
    why.

    Now, here is the same patch, except:

    a) tested under test12-pre7

    b) I suggest we explain why we return EPERM for append-only files despite
    the fact that SuS and common sense suggest EACCES.

    Facts verified under FreeBSD 4.2

    The rationale for being compatible with 4.4BSD on append-only but not on
    immutable is -- for immutable we can do the test by means of permission()
    fast but for append-only we would need an extra if() above permission so
    let's just be BSD-compatible. Alternatively, one could ignore BSD
    altogether and return EACCES in both. Or, one could ignore SuS altogether
    and return EPERM for both immutable and append-only. It is a matter of
    taste so... I chose something in the middle , perhaps non-intuitive but
    optimized for speed and the size of code.

    Regards,
    Tigran

    --- linux/fs/open.c Thu Oct 26 16:11:21 2000
    +++ work/fs/open.c Thu Dec 7 09:06:50 2000
    @@ -102,7 +102,12 @@
    goto out;
    inode = nd.dentry->d_inode;

    - error = -EACCES;
    + /* For directories it's -EISDIR, for other non-regulars - -EINVAL */
    + error = -EISDIR;
    + if (S_ISDIR(inode->i_mode))
    + goto dput_and_out;
    +
    + error = -EINVAL;
    if (!S_ISREG(inode->i_mode))
    goto dput_and_out;

    @@ -110,12 +115,9 @@
    if (error)
    goto dput_and_out;

    - error = -EROFS;
    - if (IS_RDONLY(inode))
    - goto dput_and_out;
    -
    + /* EPERM for 4.4BSD compat. EACCES would make more sense */
    error = -EPERM;
    - if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
    + if (IS_APPEND(inode))
    goto dput_and_out;

    /*
    @@ -163,7 +165,7 @@
    goto out;
    dentry = file->f_dentry;
    inode = dentry->d_inode;
    - error = -EACCES;
    + error = -EINVAL;
    if (!S_ISREG(inode->i_mode) || !(file->f_mode & FMODE_WRITE))
    goto out_putf;
    error = -EPERM;
    -
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