[PATCH] 2.2.x Fixes for stackable filesystems

From: William Taber <wtaber@rational.com>
To: torvalds@transmeta.com, alan@lxorguk.ukuu.org.uk
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] 2.2.x Fixes for stackable filesystems
Date: Thu, 26 Oct 2000 15:42:13 -0400 (EDT)	[thread overview]
Message-ID: <200010261942.PAA17381@cryolite.atria.com> (raw)

Linus, Alan,

I am proposing this patch for inclusion in the 2.2.x tree.  (Whether it goes
into 2.2.18 or 2.2.19 is your call.)  We have run this successfully with
2.2.14 through 2.2.17.

Our kernel patches help stacking file systems work properly in two
areas:

* dentry reference count fixes when files are opened by init_private_file()
* file reference count fixes for stacking filesystems mmap().

1. In some cases, stacking file systems which do no data translation may
want to substitute another dentry/inode at the time of a file open.  If
they do that, the dentry reference counts will get mishandled by some
callers of init_private_file().  Our changes make init_private_file()
take a dentry reference itself, and free it only if an error occurs on
the file open.  This leaves the file open routine free to swap the
dentry with another one.  All callers of the file system open routine
must dget() the dentry before putting it into the file structure prior
to calling the open routine.  Callers of init_private_file() must dput()
the file's dentry when they are done with the file.

2. In the mmap case, stacking file systems which do no data translation
probably want to substitute the underlying file system's file pointer,
so that paging operations are handled directly by the underlying file
system.  The call into the file system's mmap() must be allowed to set
the VM area's file pointer, so that it can effect this swap.  Our change
to the VM system is to set the VMA's file pointer only if the specific
mmap() routine did not set it.

Thanks,

Will Taber

+---------------------------------------------------------------------+
| Will Taber                                                          |
| Software Engineer, CMBU                 E-mail  wtaber@rational.com |
| Rational Software Corporation           Phone:  781-676-2436        |
| 20 Maguire Road, Lexington, Mass. 02421                             |
+---------------------------------------------------------------------+


diff -Naur linux.clean.2.2.14/fs/exec.c linux/fs/exec.c

--- linux.clean.2.2.14/fs/exec.c	Tue Oct 26 20:53:42 1999
+++ linux/fs/exec.c	Wed Sep 13 09:51:09 2000
@@ -136,7 +136,7 @@
 			goto out_fd;
 		f->f_flags = mode;
 		f->f_mode = (mode+1) & O_ACCMODE;
-		f->f_dentry = dentry;
+		f->f_dentry = dget(dentry);
 		f->f_pos = 0;
 		f->f_reada = 0;
 		f->f_op = inode->i_op->default_file_ops;
@@ -146,11 +146,11 @@
 				goto out_filp;
 		}
 		fd_install(fd, f);
-		dget(dentry);
 	}
 	return fd;
 
 out_filp:
+        dput(dentry);
 	if (error > 0)
 		error = -EIO;
 	put_filp(f);
@@ -371,6 +371,7 @@
 close_readexec:
 	if (file.f_op->release)
 		file.f_op->release(inode,&file);
+        dput(file.f_dentry);
 end_readexec:
 	return result;
 }
diff -Naur linux.clean.2.2.14/fs/file_table.c linux/fs/file_table.c
--- linux.clean.2.2.14/fs/file_table.c	Tue Jan  4 13:12:23 2000
+++ linux/fs/file_table.c	Wed Sep 13 09:51:09 2000
@@ -117,16 +117,20 @@
  */
 int init_private_file(struct file *filp, struct dentry *dentry, int mode)
 {
+	int err;
 	memset(filp, 0, sizeof(*filp));
 	filp->f_mode   = mode;
 	filp->f_count  = 1;
-	filp->f_dentry = dentry;
+	filp->f_dentry = dget(dentry);
 	filp->f_uid    = current->fsuid;
 	filp->f_gid    = current->fsgid;
 	filp->f_op     = dentry->d_inode->i_op->default_file_ops;
-	if (filp->f_op->open)
-		return filp->f_op->open(dentry->d_inode, filp);
-	else
+	if (filp->f_op->open) {
+		err = filp->f_op->open(dentry->d_inode, filp);
+                if (err)
+                    dput(dentry);
+		return err;
+        } else
 		return 0;
 }
 
diff -Naur linux.clean.2.2.14/fs/nfsd/nfsfh.c linux/fs/nfsd/nfsfh.c
--- linux.clean.2.2.14/fs/nfsd/nfsfh.c	Tue Sep 12 17:08:27 2000
+++ linux/fs/nfsd/nfsfh.c	Wed Sep 13 09:51:09 2000
@@ -396,6 +396,7 @@
 out_close:
 	if (file.f_op->release)
 		file.f_op->release(dir, &file);
+        dput(file.f_dentry);
 out:
 	return error;
 }
diff -Naur linux.clean.2.2.14/mm/mmap.c linux/mm/mmap.c
--- linux.clean.2.2.14/mm/mmap.c	Tue Jan  4 13:12:26 2000
+++ linux/mm/mmap.c	Wed Sep 13 09:51:09 2000
@@ -321,8 +321,14 @@
 			file->f_dentry->d_inode->i_writecount++;
 		if (error)
 			goto unmap_and_free_vma;
-		vma->vm_file = file;
-		file->f_count++;
+                if (vma->vm_file == NULL) {
+                    /*
+                     * underlying FS may have attached it differently--only
+                     * attach it if they didn't.
+                     */
+                    vma->vm_file = file;
+                    file->f_count++;
+                }
 	}
 
 	/*


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