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List:       linux-fsdevel
Subject:    Re: [PATCH v2 1/1] VFS permit cross device vfs_copy_file_range
From:       Olga Kornievskaia <aglo () umich ! edu>
Date:       2017-07-10 18:30:31
Message-ID: CAN-5tyHmvTy73NKMb1peEpbVu2XkM+zrXn7=WN4fw9ApgB3OSQ () mail ! gmail ! com
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Al,

Do you have plans merging this patch? I have addressed the comments
from Jeff Layton.

Thank you.

On Thu, Jul 6, 2017 at 4:58 PM, Olga Kornievskaia <aglo@umich.edu> wrote:
> Hi folks,
>
> Are there any more comments? Will this be accepted?
>
> On Fri, Jun 30, 2017 at 4:58 PM, Olga Kornievskaia <kolga@netapp.com> wrote:
>> Allow copy_file_range to copy between different superblocks but only
>> of the same file system types.
>>
>> This feature is needed by NFSv4.2 to perform file copy operation on
>> the same server or file copy between different NFSv4.2 servers.
>>
>> If a file system's fileoperations copy_file_range operation prohibits
>> cross-device copies, fall back to do_splice_direct. This would be
>> needed for the NFS (destination) server side implementation of the
>> file copy and currently for CIFS.
>>
>> Besides NFS, there is only 1 implementor of the copy_file_range FS
>> operation -- CIFS. CIFS assumes incoming file descriptors are both
>> CIFS but it will check if they are coming from different servers and
>> return error code to fall back to do_splice_direct.
>>
>> NFS will allow for copies between different NFS servers.
>>
>> Adding to the vfs.txt documentation to explicitly warn about allowing
>> for different superblocks of the same file type to be passed into the
>> copy_file_range for the future users of copy_file_range method.
>>
>> Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
>> ---
>>  Documentation/filesystems/vfs.txt |  7 +++++++
>>  fs/read_write.c                   | 13 ++++++-------
>>  2 files changed, 13 insertions(+), 7 deletions(-)
>>
>> diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
>> index f42b906..0c243f6 100644
>> --- a/Documentation/filesystems/vfs.txt
>> +++ b/Documentation/filesystems/vfs.txt
>> @@ -845,6 +845,8 @@ struct file_operations {
>>  #ifndef CONFIG_MMU
>>         unsigned (*mmap_capabilities)(struct file *);
>>  #endif
>> +       ssize_t (*copy_file_range)(struct file *, loff_t, struct file *,
>> +                                  loff_t, size_t, unsigned int);
>>  };
>>
>>  Again, all methods are called without any locks being held, unless
>> @@ -913,6 +915,11 @@ otherwise noted.
>>
>>    fallocate: called by the VFS to preallocate blocks or punch a hole.
>>
>> +  copy_file_range: called by copy_file_range(2) system call. This method
>> +                  works on two file descriptors that might reside on
>> +                  different superblocks of the same type of file system.
>> +
>> +
>>  Note that the file operations are implemented by the specific
>>  filesystem in which the inode resides. When opening a device node
>>  (character or block special) most filesystems will call special
>> diff --git a/fs/read_write.c b/fs/read_write.c
>> index 47c1d44..f981d49 100644
>> --- a/fs/read_write.c
>> +++ b/fs/read_write.c
>> @@ -1589,10 +1589,6 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>>             (file_out->f_flags & O_APPEND))
>>                 return -EBADF;
>>
>> -       /* this could be relaxed once a method supports cross-fs copies */
>> -       if (inode_in->i_sb != inode_out->i_sb)
>> -               return -EXDEV;
>> -
>>         if (len == 0)
>>                 return 0;
>>
>> @@ -1602,7 +1598,8 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>>          * Try cloning first, this is supported by more file systems, and
>>          * more efficient if both clone and copy are supported (e.g. NFS).
>>          */
>> -       if (file_in->f_op->clone_file_range) {
>> +       if (inode_in->i_sb == inode_out->i_sb &&
>> +                       file_in->f_op->clone_file_range) {
>>                 ret = file_in->f_op->clone_file_range(file_in, pos_in,
>>                                 file_out, pos_out, len);
>>                 if (ret == 0) {
>> @@ -1611,10 +1608,12 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
>>                 }
>>         }
>>
>> -       if (file_out->f_op->copy_file_range) {
>> +       if (file_out->f_op->copy_file_range &&
>> +                       (file_in->f_op->copy_file_range ==
>> +                               file_out->f_op->copy_file_range)) {
>>                 ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out,
>>                                                       pos_out, len, flags);
>> -               if (ret != -EOPNOTSUPP)
>> +               if (ret != -EOPNOTSUPP && ret != -EXDEV)
>>                         goto done;
>>         }
>>
>> --
>> 1.8.3.1
>>
>> --
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