Re: [Patch] ltt-relay-alloc mmap support (due to NFS lack ofsplice support)

[Mathieu Desnoyers]

* Masahiro Tamori (masahiro.tamori@xxxxxxxxx) wrote:
> Hello Mathieu,
> 
> I use the following version.
> LTTV 0.12.12
> LTTng 0.110
> LTT Control 0.67
> Kernles 2.6.29-rc7
> 
> The target is ARM RealviewEB.
> 
> Our customer will use NFS to store trace data not storage device for
> embedded devices.
> Since newer lttng use splice() even if NFS can not support splice(),
> I create a patch to support to mmap of ltt-relay-alloc.
> 
> I will send a mail to this mailing list for ltt-control patch.
> I do not know which mailing list should be posted for userland tools.
> 
> Best Regards,
> Masahiro Tamori
> 
> 
> ltt-relay-alloc mmap support
> 
> Splice syscall does not support NFS. We can not save trace data to
> NFS directory. If this feature is enabled, you can use mmap()
> instead of splice().
> 


Hi Masahiro,

Maybe we should consider implementing splice() support in NFS instead ?

I removed the mmap support from the ltt-relay-alloc files because splice
is more efficient and does not require to vmap the pages.  Unless there
is a strong argument telling what in NFS makes it impossible to
implement splice(), I don't really see the gain in putting back the
old mmap() mechanism we had.

Maybe the NFS people will have some information about this ?

Thanks,

Mathieu


> For embeded system, NFS must be used. Target board has not enough memory
> to save trace data and some board can not connect ATA, USB and some strage
> devices.
> 
> Signed-off-by: Masahiro.Tamori@xxxxxxxxx
> ---
>  ltt/Kconfig              |   11 	11 +	0 -	0 !
>  ltt/ltt-relay-alloc.c    |   88 	88 +	0 -	0 !
>  ltt/ltt-relay-lockless.c |   15 	15 +	0 -	0 !
>  3 files changed, 114 insertions(+)
> 
> Index: b/ltt/Kconfig
> ===================================================================
> --- a/ltt/Kconfig
> +++ b/ltt/Kconfig
> @@ -66,6 +66,17 @@ choice
> 
>  endchoice
> 
> +config LTT_RELAY_ALLOC_MMAP
> +	bool "Linux Trace Toolkit Relay mmap Support"
> +	depends on LTT_RELAY_ALLOC
> +	default y
> +	help
> +	  Support mmap for ltt-relay.
> +
> +	  Splice syscall does not support NFS. We can not save trace data to
> +          NFS directory. If this feature is enabled, you can use mmap()
> +          instead of splice().
> +
>  config LTT_SERIALIZE
>  	tristate "Linux Trace Toolkit Serializer"
>  	depends on LTT_RELAY_ALLOC
> Index: b/ltt/ltt-relay-alloc.c
> ===================================================================
> --- a/ltt/ltt-relay-alloc.c
> +++ b/ltt/ltt-relay-alloc.c
> @@ -27,6 +27,74 @@
>  static DEFINE_MUTEX(relay_channels_mutex);
>  static LIST_HEAD(relay_channels);
> 
> +#ifdef CONFIG_LTT_RELAY_ALLOC_MMAP
> +/*
> + * close() vm_op implementation for relay file mapping.
> + */
> +static void relay_file_mmap_close(struct vm_area_struct *vma)
> +{
> +}
> +
> +/*
> + * fault() vm_op implementation for relay file mapping.
> + */
> +static int relay_buf_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> +	struct page *page = NULL;
> +	struct rchan_buf *buf = vma->vm_private_data;
> +	pgoff_t pgoff = vmf->pgoff;
> +	struct page **pages;
> +
> +	if (!buf)
> +		return VM_FAULT_OOM;
> +
> +	if (pgoff >= buf->page_count)
> +		return VM_FAULT_SIGBUS;
> +
> +	pages = buf->pages;
> +	page = pages[pgoff];
> +	get_page(page);
> +	vmf->page = page;
> +
> +	return 0;
> +}
> +
> +/*
> + * vm_ops for relay file mappings.
> + */
> +static struct vm_operations_struct relay_file_mmap_ops = {
> +	.fault = relay_buf_fault,
> +	.close = relay_file_mmap_close,
> +};
> +
> +/**
> + *	relay_mmap_buf: - mmap channel buffer to process address space
> + *	@buf: relay channel buffer
> + *	@vma: vm_area_struct describing memory to be mapped
> + *
> + *	Returns 0 if ok, negative on error
> + *
> + *	Caller should already have grabbed mmap_sem.
> + */
> +static int relay_mmap_buf(struct rchan_buf *buf, struct vm_area_struct *vma)
> +{
> +	unsigned long length = vma->vm_end - vma->vm_start;
> +
> +	if (!buf)
> +		return -EBADF;
> +
> +	if (length != (unsigned long)buf->chan->alloc_size)
> +		return -EINVAL;
> +
> +	vma->vm_ops = &relay_file_mmap_ops;
> +	vma->vm_flags |= VM_DONTEXPAND;
> +	vma->vm_private_data = buf;
> +
> +	return 0;
> +}
> +
> +#endif /* CONFIG_LTT_RELAY_ALLOC_MMAP */
> +
>  /**
>   *	relay_alloc_buf - allocate a channel buffer
>   *	@buf: the buffer struct
> @@ -601,6 +669,23 @@ static int relay_file_open(struct inode
>  	return nonseekable_open(inode, filp);
>  }
> 
> +#ifdef CONFIG_LTT_RELAY_ALLOC_MMAP
> +
> +/**
> + *	relay_file_mmap - mmap file op for relay files
> + *	@filp: the file
> + *	@vma: the vma describing what to map
> + *
> + *	Calls upon relay_mmap_buf() to map the file into user space.
> + */
> +static int relay_file_mmap(struct file *filp, struct vm_area_struct *vma)
> +{
> +	struct rchan_buf *buf = filp->private_data;
> +	return relay_mmap_buf(buf, vma);
> +}
> +
> +#endif /* CONFIG_LTT_RELAY_ALLOC_MMAP */
> +
>  /**
>   *	relay_file_release - release file op for relay files
>   *	@inode: the inode
> @@ -619,6 +704,9 @@ static int relay_file_release(struct ino
> 
>  const struct file_operations ltt_relay_file_operations = {
>  	.open		= relay_file_open,
> +#ifdef CONFIG_LTT_RELAY_ALLOC_MMAP
> +	.mmap		= relay_file_mmap,
> +#endif
>  	.release	= relay_file_release,
>  };
>  EXPORT_SYMBOL_GPL(ltt_relay_file_operations);
> Index: b/ltt/ltt-relay-lockless.c
> ===================================================================
> --- a/ltt/ltt-relay-lockless.c
> +++ b/ltt/ltt-relay-lockless.c
> @@ -427,6 +427,18 @@ static int ltt_release(struct inode *ino
>  }
> 
>  /**
> + *	ltt_mmap - mmap file op for ltt files
> + *	@inode: opened inode
> + *	@file: opened file
> + *
> + *	Mmap implementation.
> + */
> +static int ltt_mmap(struct file *file,  struct vm_area_struct *vma)
> +{
> +	return ltt_relay_file_operations.mmap(file, vma);
> +}
> +
> +/**
>   *	ltt_poll - file op for ltt files
>   *	@filp: the file
>   *	@wait: poll table
> @@ -1590,6 +1602,9 @@ static struct ltt_transport ltt_relay_tr
>  static const struct file_operations ltt_file_operations = {
>  	.open = ltt_open,
>  	.release = ltt_release,
> +#ifdef CONFIG_LTT_RELAY_ALLOC_MMAP
> +	.mmap		= ltt_mmap,
> +#endif
>  	.poll = ltt_poll,
>  	.splice_read = ltt_relay_file_splice_read,
>  	.ioctl = ltt_ioctl,

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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