Re: GFS
From: Pekka J Enberg
Date: Thu Aug 11 2005 - 02:11:40 EST
Hi Mark,
On Thu, 11 Aug 2005, Pekka J Enberg wrote:
> Reading and writing from other filesystems to a GFS2 mmap'd file
> does not walk the vmas. Therefore, data consistency guarantees
> are different:
What I meant was that, if a filesystem requires vma walks, we need to do
it VFS level with something like the following patch. With this, your
filesystem would implement a_ops->iolock_acquire that sorts the locks
and takes them all. In case of GFS2, this would replace walk_vm().
Thoughts?
Pekka
[PATCH] vfs: iolock
This patch introduces iolock which can be used by filesystems that require
special locking when accessing an mmap'd region.
Unfinished and untested.
Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
---
fs/Makefile | 2 -
fs/iolock.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++
fs/read_write.c | 15 ++++++++
include/linux/fs.h | 2 +
include/linux/iolock.h | 11 ++++++
5 files changed, 117 insertions(+), 1 deletion(-)
Index: 2.6-mm/fs/iolock.c
===================================================================
--- /dev/null
+++ 2.6-mm/fs/iolock.c
@@ -0,0 +1,88 @@
+/*
+ * fs/iolock.c
+ *
+ * Derived from GFS2.
+ */
+
+#include <linux/iolock.h>
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+
+/*
+ * I/O lock contains all files that participate in locking a memory region.
+ * It is used for filesystems that require special locks to access mmap'd
+ * memory.
+ */
+struct iolock {
+ struct address_space *mapping;
+ unsigned long nr_files;
+ struct file **files;
+};
+
+struct iolock *iolock_region(const char __user *buf, size_t size)
+{
+ int err = -ENOMEM;
+ struct mm_struct *mm = current->mm;
+ struct vm_area_struct *vma;
+ unsigned long start = (unsigned long)buf;
+ unsigned long end = start + size;
+ struct iolock *ret;
+
+ ret = kcalloc(1, sizeof(*ret), GFP_KERNEL);
+ if (!ret)
+ return ERR_PTR(-ENOMEM);
+
+ down_read(&mm->mmap_sem);
+
+ ret->files = kcalloc(mm->map_count, sizeof(struct file*), GFP_KERNEL);
+ if (!ret->files)
+ goto error;
+
+ for (vma = find_vma(mm, start); vma; vma = vma->vm_next) {
+ struct file *file;
+ struct address_space *mapping;
+
+ if (end <= vma->vm_start)
+ break;
+
+ file = vma->vm_file;
+ if (!file)
+ continue;
+
+ mapping = file->f_mapping;
+ if (!mapping->a_ops->iolock_acquire ||
+ !mapping->a_ops->iolock_release)
+ continue;
+
+ /* FIXME: This only works when one address_space participates
+ in the iolock. */
+ ret->mapping = mapping;
+ ret->files[ret->nr_files++] = file;
+ }
+out:
+ up_read(&mm->mmap_sem);
+
+ if (ret->mapping->a_ops->iolock_acquire) {
+ err = ret->mapping->a_ops->iolock_acquire(ret->files, ret->nr_files);
+ if (!err)
+ goto error;
+ }
+
+ return ret;
+
+error:
+ iolock_release(ret);
+ ret = ERR_PTR(err);
+ goto out;
+}
+
+void iolock_release(struct iolock *iolock)
+{
+ struct address_space *mapping = iolock->mapping;
+ if (mapping && mapping->a_ops->iolock_release)
+ mapping->a_ops->iolock_release(iolock->files, iolock->nr_files);
+ kfree(iolock->files);
+ kfree(iolock);
+}
Index: 2.6-mm/fs/read_write.c
===================================================================
--- 2.6-mm.orig/fs/read_write.c
+++ 2.6-mm/fs/read_write.c
@@ -14,6 +14,7 @@
#include <linux/security.h>
#include <linux/module.h>
#include <linux/syscalls.h>
+#include <linux/iolock.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
@@ -247,14 +248,21 @@ ssize_t vfs_read(struct file *file, char
if (!ret) {
ret = security_file_permission (file, MAY_READ);
if (!ret) {
+ struct iolock * iolock = iolock_region(buf, count);
+ if (IS_ERR(iolock)) {
+ ret = PTR_ERR(iolock);
+ goto out;
+ }
if (file->f_op->read)
ret = file->f_op->read(file, buf, count, pos);
else
ret = do_sync_read(file, buf, count, pos);
+ iolock_release(iolock);
if (ret > 0) {
fsnotify_access(file->f_dentry);
current->rchar += ret;
}
+ out:
current->syscr++;
}
}
@@ -298,14 +306,21 @@ ssize_t vfs_write(struct file *file, con
if (!ret) {
ret = security_file_permission (file, MAY_WRITE);
if (!ret) {
+ struct iolock * iolock = iolock_region(buf, count);
+ if (IS_ERR(iolock)) {
+ ret = PTR_ERR(iolock);
+ goto out;
+ }
if (file->f_op->write)
ret = file->f_op->write(file, buf, count, pos);
else
ret = do_sync_write(file, buf, count, pos);
+ iolock_release(iolock);
if (ret > 0) {
fsnotify_modify(file->f_dentry);
current->wchar += ret;
}
+ out:
current->syscw++;
}
}
Index: 2.6-mm/include/linux/iolock.h
===================================================================
--- /dev/null
+++ 2.6-mm/include/linux/iolock.h
@@ -0,0 +1,11 @@
+#ifndef __LINUX_IOLOCK_H
+#define __LINUX_IOLOCK_H
+
+#include <linux/kernel.h>
+
+struct iolock;
+
+struct iolock *iolock_region(const char __user *buf, size_t count);
+void iolock_release(struct iolock *lock);
+
+#endif
Index: 2.6-mm/fs/Makefile
===================================================================
--- 2.6-mm.orig/fs/Makefile
+++ 2.6-mm/fs/Makefile
@@ -10,7 +10,7 @@ obj-y := open.o read_write.o file_table.
ioctl.o readdir.o select.o fifo.o locks.o dcache.o inode.o \
attr.o bad_inode.o file.o filesystems.o namespace.o aio.o \
seq_file.o xattr.o libfs.o fs-writeback.o mpage.o direct-io.o \
- ioprio.o
+ ioprio.o iolock.o
obj-$(CONFIG_INOTIFY) += inotify.o
obj-$(CONFIG_EPOLL) += eventpoll.o
Index: 2.6-mm/include/linux/fs.h
===================================================================
--- 2.6-mm.orig/include/linux/fs.h
+++ 2.6-mm/include/linux/fs.h
@@ -334,6 +334,8 @@ struct address_space_operations {
loff_t offset, unsigned long nr_segs);
struct page* (*get_xip_page)(struct address_space *, sector_t,
int);
+ int (*iolock_acquire)(struct file **, unsigned long);
+ void (*iolock_release)(struct file **, unsigned long);
};
struct backing_dev_info;
-
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