[Devel] Re: [C/R v20][PATCH 20/96] c/r: make file_pos_read/write() public

[Oren Laadan]

Nick Piggin wrote:
> On Mon, Mar 22, 2010 at 08:12:45PM -0400, Oren Laadan wrote:
>> On Mon, 22 Mar 2010, Nick Piggin wrote:
>>
>>> On Thu, Mar 18, 2010 at 08:59:45PM -0400, Oren Laadan wrote:
>>>> These two are used in the next patch when calling vfs_read/write()
>>> Said next patch didn't seem to make it to fsdevel.
>> Thanks for reviewing, and sorry about this glitch - see below.
>>
>>> Should it at least go to fs/internal.h?
>> Sure.
>>
>> So Here is the relevant hunk from said patch (the entire
>> patch is: https://patchwork.kernel.org/patch/86389/):
>>
>> +/*
>> + * Helpers to write(read) from(to) kernel space to(from) the checkpoint
>> + * image file descriptor (similar to how a core-dump is performed).
>> + *
>> + *   ckpt_kwrite() - write a kernel-space buffer to the checkpoint image
>> + *   ckpt_kread() - read from the checkpoint image to a kernel-space buffer
> 
> Hmm, OK. Slightly-more-write(2) type of write.
> 
> fs/splice.c code also has a kernel_write and readv. Not sure if there is
> any other common code. But maybe it would be better to put together some
> useful helpers under fs/ rather than a ckpt specific thing.

Right. Another place is fs/exec.c that provides kernel_read().
I'll put the common code in kernel/read_write.c then.

Oren.

> 
>> + */
>> +
>> +static inline int _ckpt_kwrite(struct file *file, void *addr, int count)
>> +{
>> +	void __user *uaddr = (__force void __user *) addr;
>> +	ssize_t nwrite;
>> +	int nleft;
>> +
>> +	for (nleft = count; nleft; nleft -= nwrite) {
>> +		loff_t pos = file_pos_read(file);
>> +		nwrite = vfs_write(file, uaddr, nleft, &pos);
>> +		file_pos_write(file, pos);
>> +		if (nwrite < 0) {
>> +			if (nwrite == -EAGAIN)
>> +				nwrite = 0;
>> +			else
>> +				return nwrite;
>> +		}
>> +		uaddr += nwrite;
>> +	}
>> +	return 0;
>> +}
>> +
>> +int ckpt_kwrite(struct ckpt_ctx *ctx, void *addr, int count)
>> +{
>> +	mm_segment_t fs;
>> +	int ret;
>> +
>> +	fs = get_fs();
>> +	set_fs(KERNEL_DS);
>> +	ret = _ckpt_kwrite(ctx->file, addr, count);
>> +	set_fs(fs);
>> +
>> +	ctx->total += count;
>> +	return ret;
>> +}
>> +
>> +static inline int _ckpt_kread(struct file *file, void *addr, int count)
>> +{
>> +	void __user *uaddr = (__force void __user *) addr;
>> +	ssize_t nread;
>> +	int nleft;
>> +
>> +	for (nleft = count; nleft; nleft -= nread) {
>> +		loff_t pos = file_pos_read(file);
>> +		nread = vfs_read(file, uaddr, nleft, &pos);
>> +		file_pos_write(file, pos);
>> +		if (nread <= 0) {
>> +			if (nread == -EAGAIN) {
>> +				nread = 0;
>> +				continue;
>> +			} else if (nread == 0)
>> +				nread = -EPIPE;		/* unexecpted EOF */
>> +			return nread;
>> +		}
>> +		uaddr += nread;
>> +	}
>> +	return 0;
>> +}
>> +
>> +int ckpt_kread(struct ckpt_ctx *ctx, void *addr, int count)
>> +{
>> +	mm_segment_t fs;
>> +	int ret;
>> +
>> +	fs = get_fs();
>> +	set_fs(KERNEL_DS);
>> +	ret = _ckpt_kread(ctx->file , addr, count);
>> +	set_fs(fs);
>> +
>> +	ctx->total += count;
>> +	return ret;
>> +}
>>
>> Oren.
>> --
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> 
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