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SubjectRe: [patch 1/1] sys_sync_file_range()
Neil Brown <neilb@suse.de> wrote:
>
> Hmmm... any chance this could be split into a sys_sync_file_range and
> a vfs_sync_file_range which takes a 'struct file*' and does less (or
> no) sanity checking, so I can call it from nfsd?

Problem is, we don't appear to have a way of syncing the file's metadata
without also syncing all of its pagecache.

For example, ext3_sync_file() will run a commit, which will sync all data
and metadata.

ext2_sync_file() will also sync all pagecache as well as metadata. Even
though do_fsync() already synced the file data (!).


Is the below still useful?


diff -puN mm/fadvise.c~sys_sync_file_range mm/fadvise.c
--- devel/mm/fadvise.c~sys_sync_file_range 2006-03-29 23:48:28.000000000 -0800
+++ devel-akpm/mm/fadvise.c 2006-03-29 23:48:28.000000000 -0800
@@ -35,17 +35,6 @@
*
* LINUX_FADV_ASYNC_WRITE: push some or all of the dirty pages at the disk.
*
- * LINUX_FADV_WRITE_WAIT, LINUX_FADV_ASYNC_WRITE: push all of the currently
- * dirty pages at the disk.
- *
- * LINUX_FADV_WRITE_WAIT, LINUX_FADV_ASYNC_WRITE, LINUX_FADV_WRITE_WAIT: push
- * all of the currently dirty pages at the disk, wait until they have been
- * written.
- *
- * It should be noted that none of these operations write out the file's
- * metadata. So unless the application is strictly performing overwrites of
- * already-instantiated disk blocks, there are no guarantees here that the data
- * will be available after a crash.
*/
asmlinkage long sys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice)
{
@@ -129,15 +118,6 @@ asmlinkage long sys_fadvise64_64(int fd,
invalidate_mapping_pages(mapping, start_index,
end_index);
break;
- case LINUX_FADV_ASYNC_WRITE:
- ret = __filemap_fdatawrite_range(mapping, offset, endbyte,
- WB_SYNC_NONE);
- break;
- case LINUX_FADV_WRITE_WAIT:
- ret = wait_on_page_writeback_range(mapping,
- offset >> PAGE_CACHE_SHIFT,
- endbyte >> PAGE_CACHE_SHIFT);
- break;
default:
ret = -EINVAL;
}
diff -puN include/linux/fadvise.h~sys_sync_file_range include/linux/fadvise.h
--- devel/include/linux/fadvise.h~sys_sync_file_range 2006-03-29 23:48:28.000000000 -0800
+++ devel-akpm/include/linux/fadvise.h 2006-03-29 23:48:28.000000000 -0800
@@ -18,10 +18,4 @@
#define POSIX_FADV_NOREUSE 5 /* Data will be accessed once. */
#endif

-/*
- * Linux-specific fadvise() extensions:
- */
-#define LINUX_FADV_ASYNC_WRITE 32 /* Start writeout on range */
-#define LINUX_FADV_WRITE_WAIT 33 /* Wait upon writeout to range */
-
#endif /* FADVISE_H_INCLUDED */
diff -puN /dev/null fs/sync.c
--- /dev/null 2003-09-15 06:40:47.000000000 -0700
+++ devel-akpm/fs/sync.c 2006-03-30 00:16:37.000000000 -0800
@@ -0,0 +1,163 @@
+/*
+ * High-level sync()-related operations
+ */
+
+#include <linux/kernel.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/writeback.h>
+#include <linux/syscalls.h>
+#include <linux/linkage.h>
+#include <linux/pagemap.h>
+
+#define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \
+ SYNC_FILE_RANGE_WAIT_AFTER)
+
+/*
+ * sys_sync_file_range() permits finely controlled syncing over a segment of
+ * a file in the range offset .. (offset+nbytes-1) inclusive. If nbytes is
+ * zero then sys_sync_file_range() will operate from offset out to EOF.
+ *
+ * The flag bits are:
+ *
+ * SYNC_FILE_RANGE_WAIT_BEFORE: wait upon writeout of all pages in the range
+ * before performing the write.
+ *
+ * SYNC_FILE_RANGE_WRITE: initiate writeout of all those dirty pages in the
+ * range which are not presently under writeback.
+ *
+ * SYNC_FILE_RANGE_WAIT_AFTER: wait upon writeout of all pages in the range
+ * after performing the write.
+ *
+ * Useful combinations of the flag bits are:
+ *
+ * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE: ensures that all pages
+ * in the range which were dirty on entry to sys_sync_file_range() are placed
+ * under writeout. This is a start-write-for-data-integrity operation.
+ *
+ * SYNC_FILE_RANGE_WRITE: start writeout of all dirty pages in the range which
+ * are not presently under writeout. This is an asynchronous flush-to-disk
+ * operation. Not suitable for data integrity operations.
+ *
+ * SYNC_FILE_RANGE_WAIT_BEFORE (or SYNC_FILE_RANGE_WAIT_AFTER): wait for
+ * completion of writeout of all pages in the range. This will be used after an
+ * earlier SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE operation to wait
+ * for that operation to complete and to return the result.
+ *
+ * SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE|SYNC_FILE_RANGE_WAIT_AFTER:
+ * a traditional sync() operation. This is a write-for-data-integrity operation
+ * which will ensure that all pages in the range which were dirty on entry to
+ * sys_sync_file_range() are committed to disk.
+ *
+ *
+ * SYNC_FILE_RANGE_WAIT_BEFORE and SYNC_FILE_RANGE_WAIT_AFTER will detect any
+ * I/O errors or ENOSPC conditions and will return those to the caller, after
+ * clearing the EIO and ENOSPC flags in the address_space.
+ *
+ * It should be noted that none of these operations write out the file's
+ * metadata. So unless the application is strictly performing overwrites of
+ * already-instantiated disk blocks, there are no guarantees here that the data
+ * will be available after a crash.
+ */
+asmlinkage long sys_sync_file_range(int fd, loff_t offset, loff_t nbytes,
+ int flags)
+{
+ int ret;
+ struct file *file;
+ loff_t endbyte; /* inclusive */
+ int fput_needed;
+
+ ret = -EINVAL;
+ if (flags & ~VALID_FLAGS)
+ goto out;
+
+ endbyte = offset + nbytes;
+
+ if ((s64)offset < 0)
+ goto out;
+ if ((s64)endbyte < 0)
+ goto out;
+ if (endbyte < offset)
+ goto out;
+
+ if (sizeof(pgoff_t) == 4) {
+ if (offset >= (0x100000000ULL << PAGE_CACHE_SHIFT)) {
+ /*
+ * The range starts outside a 32 bit machine's
+ * pagecache addressing capabilities. Let it "succeed"
+ */
+ ret = 0;
+ goto out;
+ }
+ if (endbyte >= (0x100000000ULL << PAGE_CACHE_SHIFT)) {
+ /*
+ * Out to EOF
+ */
+ nbytes = 0;
+ }
+ }
+
+ if (nbytes == 0)
+ endbyte = -1;
+ else
+ endbyte--; /* inclusive */
+
+ file = fget_light(fd, &fput_needed);
+ if (!file) {
+ ret = -EBADF;
+ goto out;
+ }
+
+ if (S_ISFIFO(file->f_dentry->d_inode->i_mode)) {
+ ret = -ESPIPE;
+ goto out_put;
+ }
+
+ ret = do_sync_file_range(file, offset, endbyte, flags);
+out_put:
+ fput_light(file, fput_needed);
+out:
+ return ret;
+}
+
+/*
+ * `endbyte' is inclusive
+ */
+int do_sync_file_range(struct file *file, loff_t offset, loff_t endbyte,
+ int flags)
+{
+ int ret;
+ struct address_space *mapping;
+
+ mapping = file->f_mapping;
+ if (!mapping) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ ret = 0;
+ if (flags & SYNC_FILE_RANGE_WAIT_BEFORE) {
+ ret = wait_on_page_writeback_range(mapping,
+ offset >> PAGE_CACHE_SHIFT,
+ endbyte >> PAGE_CACHE_SHIFT);
+ if (ret < 0)
+ goto out;
+ }
+
+ if (flags & SYNC_FILE_RANGE_WRITE) {
+ ret = __filemap_fdatawrite_range(mapping, offset, endbyte,
+ WB_SYNC_NONE);
+ if (ret < 0)
+ goto out;
+ }
+
+ if (flags & SYNC_FILE_RANGE_WAIT_AFTER) {
+ ret = wait_on_page_writeback_range(mapping,
+ offset >> PAGE_CACHE_SHIFT,
+ endbyte >> PAGE_CACHE_SHIFT);
+ }
+out:
+ return ret;
+}
+EXPORT_SYMBOL_GPL(do_sync_file_range);
diff -puN include/linux/syscalls.h~sys_sync_file_range include/linux/syscalls.h
--- devel/include/linux/syscalls.h~sys_sync_file_range 2006-03-29 23:48:28.000000000 -0800
+++ devel-akpm/include/linux/syscalls.h 2006-03-30 00:11:50.000000000 -0800
@@ -569,5 +569,7 @@ asmlinkage long compat_sys_newfstatat(un
asmlinkage long compat_sys_openat(unsigned int dfd, const char __user *filename,
int flags, int mode);
asmlinkage long sys_unshare(unsigned long unshare_flags);
+asmlinkage long sys_sync_file_range(int fd, loff_t offset, loff_t nbytes,
+ int flags);

#endif
diff -puN include/linux/fs.h~sys_sync_file_range include/linux/fs.h
--- devel/include/linux/fs.h~sys_sync_file_range 2006-03-29 23:48:28.000000000 -0800
+++ devel-akpm/include/linux/fs.h 2006-03-30 00:15:44.000000000 -0800
@@ -757,6 +757,13 @@ extern void send_sigio(struct fown_struc
extern int fcntl_setlease(unsigned int fd, struct file *filp, long arg);
extern int fcntl_getlease(struct file *filp);

+/* fs/sync.c */
+#define SYNC_FILE_RANGE_WAIT_BEFORE 1
+#define SYNC_FILE_RANGE_WRITE 2
+#define SYNC_FILE_RANGE_WAIT_AFTER 4
+extern int do_sync_file_range(struct file *file, loff_t offset, loff_t endbyte,
+ int flags);
+
/* fs/locks.c */
extern void locks_init_lock(struct file_lock *);
extern void locks_copy_lock(struct file_lock *, struct file_lock *);
diff -puN fs/Makefile~sys_sync_file_range fs/Makefile
--- devel/fs/Makefile~sys_sync_file_range 2006-03-29 23:48:28.000000000 -0800
+++ devel-akpm/fs/Makefile 2006-03-30 00:11:47.000000000 -0800
@@ -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 pnode.o drop_caches.o
+ ioprio.o pnode.o drop_caches.o sync.o

obj-$(CONFIG_INOTIFY) += inotify.o
obj-$(CONFIG_EPOLL) += eventpoll.o
diff -puN include/asm-i386/unistd.h~sys_sync_file_range include/asm-i386/unistd.h
--- devel/include/asm-i386/unistd.h~sys_sync_file_range 2006-03-29 23:48:28.000000000 -0800
+++ devel-akpm/include/asm-i386/unistd.h 2006-03-29 23:48:28.000000000 -0800
@@ -318,8 +318,9 @@
#define __NR_unshare 310
#define __NR_set_robust_list 311
#define __NR_get_robust_list 312
+#define __NR_sys_sync_file_range 313

-#define NR_syscalls 313
+#define NR_syscalls 314

/*
* user-visible error numbers are in the range -1 - -128: see
diff -puN arch/i386/kernel/syscall_table.S~sys_sync_file_range arch/i386/kernel/syscall_table.S
--- devel/arch/i386/kernel/syscall_table.S~sys_sync_file_range 2006-03-29 23:48:28.000000000 -0800
+++ devel-akpm/arch/i386/kernel/syscall_table.S 2006-03-29 23:48:28.000000000 -0800
@@ -312,3 +312,4 @@ ENTRY(sys_call_table)
.long sys_unshare /* 310 */
.long sys_set_robust_list
.long sys_get_robust_list
+ .long sys_sync_file_range
_
-
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