linux-ext4 - Re: [PATCH 1/3] fs: Create __block_page_mkwrite() helper passing error values back

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Date:	Tue, 17 May 2011 11:09:03 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 1/3] fs: Create __block_page_mkwrite() helper passing
 error values back

> +	if (unlikely(ret < 0))
>  		unlock_page(page);
> +	else
>  		ret = VM_FAULT_LOCKED;
>  out:
>  	return ret;

Using two different types of return values here seems rather unclean.
I'd rather use 0 instead of VM_FAULT_LOCKED here, and maybe overload
-EAGAIN for VM_FAULT_NOPAGE.

> +int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
> +		   get_block_t get_block)
> +{
> +	int ret = __block_page_mkwrite(vma, vmf, get_block);
> +
> +	if (unlikely(ret < 0)) {
> +		if (ret == -ENOMEM)
> +			return VM_FAULT_OOM;
> +		/* -ENOSPC, -EIO, etc */
> +		return VM_FAULT_SIGBUS;
> +	}
> +	return ret;

and maybe also add a small inlined block_page_mkwrite_error helper
to translate the values.

Alternatively it might make sense to add a VM_FAULT_ENOSPC return value
so that you could re-use block_page_mkwrite unmodified, and we could
also have better error reporting for that case for the core VM.

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