Dave Kleikamp wrote:

On Thu, 2007-03-01 at 14:59 -0800, Andrew Morton wrote:

quoted

On Thu, 01 Mar 2007 22:44:16 +0000
Dave Kleikamp [off-list ref] wrote:

quoted

On Thu, 2007-03-01 at 14:25 -0800, Andrew Morton wrote:

quoted

On Fri, 2 Mar 2007 00:04:45 +0530
"Amit K. Arora" [off-list ref] wrote:

quoted

quoted

+asmlinkage long sys_fallocate(int fd, loff_t offset, loff_t len)
+{
+	struct file *file;
+	struct inode *inode;
+	long ret = -EINVAL;
+	file = fget(fd);
+	if (!file)
+		goto out;
+	inode = file->f_path.dentry->d_inode;
+	if (inode->i_op && inode->i_op->fallocate)
+		ret = inode->i_op->fallocate(inode, offset, len);
+	else
+		ret = -ENOTTY;
+	fput(file);
+out:
+        return ret;
+}

ENOTTY is a bit unconventional - we often use EINVAL for this sort of
thing.  But EINVAL has other meanings for posix_fallocate() and isn't
really appropriate here anyway.  So I'm not sure what would be better...

Would EINVAL (or whatever) make it back to the caller of
posix_fallocate(), or would glibc fall back to its current
implementation?

Forgive me if I haven't put enough thought into it, but would it be
useful to create a generic_fallocate() that writes zeroed pages for any
non-existent pages in the range?  I don't know how glibc currently
implements posix_fallocate(), but maybe the kernel could do it more
efficiently, even in generic code.  Maybe we don't care, since the major
file systems can probably do something better in their own code.

Given that glibc already implements fallocate for all filesystems, it will
need to continue to do so for filesystems which don't implement this
syscall - otherwise applications would start breaking.

I didn't make it clear, but my point was to call generic_fallocate if
the file system did not define i_op->allocate().

if (inode->i_op && inode->i_op->fallocate)
	ret = inode->i_op->fallocate(inode, offset, len);
else
	ret = generic_fallocate(inode, offset, len);

I'm not sure it's worth the effort, but I thought I'd throw the idea out
there.

I think this is useful.

Mingming