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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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