On Tue, Aug 12, 2014 at 11:34 PM, Shirish Pargaonkar
<shirishpargaonkar@xxxxxxxxx> wrote:
> On Tue, Aug 12, 2014 at 9:13 AM, Steve French <smfrench@xxxxxxxxx> wrote:
>> Many Linux filesystems make a file "sparse" when extending
>> a file with ftruncate. This does work for CIFS to Samba
>> (only) but not for SMB2/SMB3 (to Samba or Windows) since
>> there is a "set sparse" fsctl which is supposed to be
>> sent to mark a file as sparse.
>>
>> This patch marks a file as sparse by sending this simple
>> set sparse fsctl if it is extended more than 2 pages.
>> It has been tested to Windows 8.1, Samba and various
>> SMB2/SMB3 servers which do support setting sparse (and
>> MacOS which does not appear to support the fsctl yet).
>> If a server share does not support setting a file
>> as sparse, then we do not retry setting sparse on that
>> share.
>>
>> The disk space savings for sparse files can be quite
>> large (even more significant on Windows servers than Samba).
>>
>> Signed-off-by: Steve French <smfrench@xxxxxxxxx>
>> ---
>> fs/cifs/cifsglob.h | 1 +
>> fs/cifs/smb2ops.c | 43 +++++++++++++++++++++++++++++++++++++++++++
>> fs/cifs/smb2pdu.c | 4 +++-
>> 3 files changed, 47 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
>> index 0012e1e..bc20a6e 100644
>> --- a/fs/cifs/cifsglob.h
>> +++ b/fs/cifs/cifsglob.h
>> @@ -883,6 +883,7 @@ struct cifs_tcon {
>> for this mount even if server would support */
>> bool local_lease:1; /* check leases (only) on local system not remote */
>> bool broken_posix_open; /* e.g. Samba server versions < 3.3.2, 3.2.9 */
>> + bool broken_sparse_sup; /* if server or share does not support sparse */
>> bool need_reconnect:1; /* connection reset, tid now invalid */
>> #ifdef CONFIG_CIFS_SMB2
>> bool print:1; /* set if connection to printer share */
>> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
>> index 77f8aeb..7463436 100644
>> --- a/fs/cifs/smb2ops.c
>> +++ b/fs/cifs/smb2ops.c
>> @@ -736,6 +736,49 @@ smb2_set_file_size(const unsigned int xid, struct
>> cifs_tcon *tcon,
>> struct cifsFileInfo *cfile, __u64 size, bool set_alloc)
>> {
>> __le64 eof = cpu_to_le64(size);
>> + struct inode *inode;
>> +
>> + /*
>> + * If extending file more than one page make sparse. Many Linux fs
>> + * make files sparse by default when extending via ftruncate
>> + */
>> + inode = cfile->dentry->d_inode;
>> +
>> + if (!set_alloc && (size > inode->i_size + 8192)) {
>> + struct cifsInodeInfo *cifsi;
>> + __u8 set_sparse = 1;
>> + int rc;
>> +
>> + cifsi = CIFS_I(inode);
>> +
>> + /* if file already sparse or no server support don't bother */
>> + if (cifsi->cifsAttrs & FILE_ATTRIBUTE_SPARSE_FILE)
>> + goto smb2_set_eof;
>
> Is this check always valid? Is it possible that the file is not
> sparse anymore at the server?
If someone unsparsed the file that is fine. The ftruncate to
extend the file will still work fine as it did before this patch
(it just will take up more disk space than it would
if the file were sparse). When the actimeo (1 second) expires,
and we next refresh the inode attributes from the server
we will notice the file is not sparse and and future
ftruncate/extends will mark the file sparse.
>
>> +
>> + /*
>> + * Can't check for sparse support on share the usual way via the
>> + * FS attribute info (FILE_SUPPORTS_SPARSE_FILES) on the share
>> + * since Samba server doesn't set the flag on the share, yet
>> + * supports the set sparse FSCTL and returns sparse correctly
>> + * in the file attributes. If we fail setting sparse though we
>> + * mark that server does not support sparse files for this share
>> + * to avoid repeatedly sending the unsupported fsctl to server
>> + * if the file is repeatedly extended.
>> + */
>> + if (tcon->broken_sparse_sup)
>> + goto smb2_set_eof;
>> +
>> + rc = SMB2_ioctl(xid, tcon, cfile->fid.persistent_fid,
>> + cfile->fid.volatile_fid, FSCTL_SET_SPARSE,
>> + true /* is_fctl */, &set_sparse, 1, NULL, NULL);
>> + if (rc) {
>> + tcon->broken_sparse_sup = true;
>> + cifs_dbg(FYI, "set sparse rc = %d\n", rc);
>> + } else
>> + cifsi->cifsAttrs |= FILE_ATTRIBUTE_SPARSE_FILE;
>> + }
>> +
>> +smb2_set_eof:
>> return SMB2_set_eof(xid, tcon, cfile->fid.persistent_fid,
>> cfile->fid.volatile_fid, cfile->pid, &eof, false);
>> }
--
Thanks,
Steve
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