Re: [PATCH v3 8/9] vfs: copy_file_range() can do a pagecache copy with splice

[Anna Schumaker <Anna.Schumaker-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org>]

On 09/28/2015 02:31 PM, Darrick J. Wong wrote:
> On Fri, Sep 25, 2015 at 04:48:14PM -0400, Anna Schumaker wrote:
>> The NFS server will need some kind offallback for filesystems that don't
> 
> "some kind of fallback"

I'll rephrase that :)

> 
>> have any kind of copy acceleration, and it should be generally useful to
>> have an in-kernel copy to avoid lots of switches between kernel and user
>> space.
>>
>> I make this configurable by adding two new flags.  Users who only want a
>> reflink can pass COPY_FR_REFLINK, and users who want a full data copy can
>> pass COPY_FR_COPY.  The default (flags=0) means to first attempt a
>> reflink, but use the pagecache if that fails.
> 
> "The COPY_FR_DEDUPE flag makes a reflink, but only if the contents of both
> file ranges are identical."

Sure.  I'll point that out in the man page.

> 
>> I moved the rw_verify_area() calls into the fallback code since some
>> filesystems can handle reflinking a large range.
>>
>> Signed-off-by: Anna Schumaker <Anna.Schumaker-ZwjVKphTwtPQT0dZR+AlfA@public.gmane.org>
>> ---
>> v3:
>> - Check that both filesystems have the same filesystem type
>> - Add COPY_FR_DEDUPE flag for Darrick
>> - Check that at most one flag is set at a time
>> ---
>>  fs/read_write.c           | 61 +++++++++++++++++++++++++++++++----------------
>>  include/linux/copy.h      |  6 +++++
>>  include/uapi/linux/Kbuild |  1 +
>>  include/uapi/linux/copy.h |  8 +++++++
>>  4 files changed, 56 insertions(+), 20 deletions(-)
>>  create mode 100644 include/linux/copy.h
>>  create mode 100644 include/uapi/linux/copy.h
>>
>> diff --git a/fs/read_write.c b/fs/read_write.c
>> index ee9fa37..a0fd9dc 100644
>> --- a/fs/read_write.c
>> +++ b/fs/read_write.c
>> @@ -7,6 +7,7 @@
>>  #include <linux/slab.h> 
>>  #include <linux/stat.h>
>>  #include <linux/fcntl.h>
>> +#include <linux/copy.h>
>>  #include <linux/file.h>
>>  #include <linux/uio.h>
>>  #include <linux/fsnotify.h>
>> @@ -1329,6 +1330,29 @@ COMPAT_SYSCALL_DEFINE4(sendfile64, int, out_fd, int, in_fd,
>>  }
>>  #endif
>>  
>> +static ssize_t vfs_copy_file_pagecache(struct file *file_in, loff_t pos_in,
>> +				       struct file *file_out, loff_t pos_out,
>> +				       size_t len)
>> +{
>> +	ssize_t ret;
>> +
>> +	ret = rw_verify_area(READ, file_in, &pos_in, len);
>> +	if (ret >= 0) {
>> +		len = ret;
>> +		ret = rw_verify_area(WRITE, file_out, &pos_out, len);
>> +		if (ret >= 0)
>> +			len = ret;
>> +	}
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	file_start_write(file_out);
>> +	ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out, len, 0);
>> +	file_end_write(file_out);
>> +
>> +	return ret;
>> +}
>> +
>>  /*
>>   * copy_file_range() differs from regular file read and write in that it
>>   * specifically allows return partial success.  When it does so is up to
>> @@ -1338,34 +1362,26 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>>  			    struct file *file_out, loff_t pos_out,
>>  			    size_t len, unsigned int flags)
>>  {
>> -	struct inode *inode_in;
>> -	struct inode *inode_out;
>>  	ssize_t ret;
>>  
>> -	if (flags)
>> +	/* Flags should only be used exclusively. */
>> +	if ((flags & COPY_FR_COPY) && (flags & ~COPY_FR_COPY))
>>  		return -EINVAL;
>> +	if ((flags & COPY_FR_REFLINK) && (flags & ~COPY_FR_REFLINK))
>> +		return -EINVAL;
>> +	if (flags & COPY_FR_DEDUPE)
>> +		return -EOPNOTSUPP;
> 
> Since dedupe can't be combined with copy or reflink either, we might as well
> say:
> 
> if ((flags & COPY_FR_DEDUPE) && (flags & ~COPY_FR_DEDUPE))
> 	return -EINVAL;
> 
> and let the per-fs copy_file_range()s dispatch appropriately.

That makes sense.  I was thinking that could be changed when dedupe is added, but I guess that defeats the purpose of adding the flag during the initial merge.

Anna

> 
> Otherwise, you can add:
> Reviewed-by: Darrick J. Wong <darrick.wong-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> 
> --D
> 
>>  
>> -	/* copy_file_range allows full ssize_t len, ignoring MAX_RW_COUNT  */
>> -	ret = rw_verify_area(READ, file_in, &pos_in, len);
>> -	if (ret >= 0)
>> -		ret = rw_verify_area(WRITE, file_out, &pos_out, len);
>> -	if (ret < 0)
>> -		return ret;
>> +	/* Default behavior is to try both. */
>> +	if (flags == 0)
>> +		flags = COPY_FR_COPY | COPY_FR_REFLINK;
>>  
>>  	if (!(file_in->f_mode & FMODE_READ) ||
>>  	    !(file_out->f_mode & FMODE_WRITE) ||
>>  	    (file_out->f_flags & O_APPEND) ||
>> -	    !file_out->f_op || !file_out->f_op->copy_file_range)
>> +	    !file_out->f_op)
>>  		return -EBADF;
>>  
>> -	inode_in = file_inode(file_in);
>> -	inode_out = file_inode(file_out);
>> -
>> -	/* make sure offsets don't wrap and the input is inside i_size */
>> -	if (pos_in + len < pos_in || pos_out + len < pos_out ||
>> -	    pos_in + len > i_size_read(inode_in))
>> -		return -EINVAL;
>> -
>>  	if (len == 0)
>>  		return 0;
>>  
>> @@ -1373,8 +1389,13 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>>  	if (ret)
>>  		return ret;
>>  
>> -	ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out, pos_out,
>> -					      len, flags);
>> +	ret = -EOPNOTSUPP;
>> +	if (file_out->f_op->copy_file_range && (file_in->f_op == file_out->f_op))
>> +		ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out,
>> +						      pos_out, len, flags);
>> +	if ((ret < 0) && (flags & COPY_FR_COPY))
>> +		ret = vfs_copy_file_pagecache(file_in, pos_in, file_out,
>> +					      pos_out, len);
>>  	if (ret > 0) {
>>  		fsnotify_access(file_in);
>>  		add_rchar(current, ret);
>> diff --git a/include/linux/copy.h b/include/linux/copy.h
>> new file mode 100644
>> index 0000000..fd54543
>> --- /dev/null
>> +++ b/include/linux/copy.h
>> @@ -0,0 +1,6 @@
>> +#ifndef _LINUX_COPY_H
>> +#define _LINUX_COPY_H
>> +
>> +#include <uapi/linux/copy.h>
>> +
>> +#endif /* _LINUX_COPY_H */
>> diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild
>> index f7b2db4..faafd67 100644
>> --- a/include/uapi/linux/Kbuild
>> +++ b/include/uapi/linux/Kbuild
>> @@ -90,6 +90,7 @@ header-y += coda_psdev.h
>>  header-y += coff.h
>>  header-y += connector.h
>>  header-y += const.h
>> +header-y += copy.h
>>  header-y += cramfs_fs.h
>>  header-y += cuda.h
>>  header-y += cyclades.h
>> diff --git a/include/uapi/linux/copy.h b/include/uapi/linux/copy.h
>> new file mode 100644
>> index 0000000..6225838
>> --- /dev/null
>> +++ b/include/uapi/linux/copy.h
>> @@ -0,0 +1,8 @@
>> +#ifndef _UAPI_LINUX_COPY_H
>> +#define _UAPI_LINUX_COPY_H
>> +
>> +#define COPY_FR_COPY		(1 << 0)  /* Only do a pagecache copy.  */
>> +#define COPY_FR_REFLINK		(1 << 1)  /* Only make a reflink.       */
>> +#define COPY_FR_DEDUPE		(1 << 2)  /* Deduplicate file data.     */
>> +
>> +#endif /* _UAPI_LINUX_COPY_H */
>> -- 
>> 2.5.3
>>
>> --
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