3 files changed, 99 insertions, 0 deletions

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index d0cb042732cb..f5fcd6360056 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -878,6 +878,9 @@ out:
 
 static loff_t cifs_llseek(struct file *file, loff_t offset, int whence)
 {
+        struct cifsFileInfo *cfile = file->private_data;
+        struct cifs_tcon *tcon;
+
         /*
          * whence == SEEK_END || SEEK_DATA || SEEK_HOLE => we must revalidate
          * the cached file length
@@ -909,6 +912,12 @@ static loff_t cifs_llseek(struct file *file, loff_t offset, int whence)
                 if (rc < 0)
                         return (loff_t)rc;
         }
+        if (cfile && cfile->tlink) {
+                tcon = tlink_tcon(cfile->tlink);
+                if (tcon->ses->server->ops->llseek)
+                        return tcon->ses->server->ops->llseek(file, tcon,
+                                                              offset, whence);
+        }
         return generic_file_llseek(file, offset, whence);
 }
 
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 33c251b408aa..334ff5f9c3f3 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -497,6 +497,8 @@ struct smb_version_operations {
         /* version specific fiemap implementation */
         int (*fiemap)(struct cifs_tcon *tcon, struct cifsFileInfo *,
                       struct fiemap_extent_info *, u64, u64);
+        /* version specific llseek implementation */
+        loff_t (*llseek)(struct file *, struct cifs_tcon *, loff_t, int);
 };
 
 struct smb_version_values {
diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 542b50c0b292..e921e6511728 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -2922,6 +2922,90 @@ static long smb3_simple_falloc(struct file *file, struct cifs_tcon *tcon,
         return rc;
 }
 
+static loff_t smb3_llseek(struct file *file, struct cifs_tcon *tcon, loff_t offset, int whence)
+{
+        struct cifsFileInfo *wrcfile, *cfile = file->private_data;
+        struct cifsInodeInfo *cifsi;
+        struct inode *inode;
+        int rc = 0;
+        struct file_allocated_range_buffer in_data, *out_data = NULL;
+        u32 out_data_len;
+        unsigned int xid;
+
+        if (whence != SEEK_HOLE && whence != SEEK_DATA)
+                return generic_file_llseek(file, offset, whence);
+
+        inode = d_inode(cfile->dentry);
+        cifsi = CIFS_I(inode);
+
+        if (offset < 0 || offset >= i_size_read(inode))
+                return -ENXIO;
+
+        xid = get_xid();
+        /*
+         * We need to be sure that all dirty pages are written as they
+         * might fill holes on the server.
+         * Note that we also MUST flush any written pages since at least
+         * some servers (Windows2016) will not reflect recent writes in
+         * QUERY_ALLOCATED_RANGES until SMB2_flush is called.
+         */
+        wrcfile = find_writable_file(cifsi, false);
+        if (wrcfile) {
+                filemap_write_and_wait(inode->i_mapping);
+                smb2_flush_file(xid, tcon, &wrcfile->fid);
+                cifsFileInfo_put(wrcfile);
+        }
+
+        if (!(cifsi->cifsAttrs & FILE_ATTRIBUTE_SPARSE_FILE)) {
+                if (whence == SEEK_HOLE)
+                        offset = i_size_read(inode);
+                goto lseek_exit;
+        }
+
+        in_data.file_offset = cpu_to_le64(offset);
+        in_data.length = cpu_to_le64(i_size_read(inode));
+
+        rc = SMB2_ioctl(xid, tcon, cfile->fid.persistent_fid,
+                        cfile->fid.volatile_fid,
+                        FSCTL_QUERY_ALLOCATED_RANGES, true,
+                        (char *)&in_data, sizeof(in_data),
+                        sizeof(struct file_allocated_range_buffer),
+                        (char **)&out_data, &out_data_len);
+        if (rc == -E2BIG)
+                rc = 0;
+        if (rc)
+                goto lseek_exit;
+
+        if (whence == SEEK_HOLE && out_data_len == 0)
+                goto lseek_exit;
+
+        if (whence == SEEK_DATA && out_data_len == 0) {
+                rc = -ENXIO;
+                goto lseek_exit;
+        }
+
+        if (out_data_len < sizeof(struct file_allocated_range_buffer)) {
+                rc = -EINVAL;
+                goto lseek_exit;
+        }
+        if (whence == SEEK_DATA) {
+                offset = le64_to_cpu(out_data->file_offset);
+                goto lseek_exit;
+        }
+        if (offset < le64_to_cpu(out_data->file_offset))
+                goto lseek_exit;
+
+        offset = le64_to_cpu(out_data->file_offset) + le64_to_cpu(out_data->length);
+
+ lseek_exit:
+        free_xid(xid);
+        kfree(out_data);
+        if (!rc)
+                return vfs_setpos(file, offset, inode->i_sb->s_maxbytes);
+        else
+                return rc;
+}
+
 static int smb3_fiemap(struct cifs_tcon *tcon,
                        struct cifsFileInfo *cfile,
                        struct fiemap_extent_info *fei, u64 start, u64 len)
@@ -4166,6 +4250,7 @@ struct smb_version_operations smb20_operations = {
         .ioctl_query_info = smb2_ioctl_query_info,
         .make_node = smb2_make_node,
         .fiemap = smb3_fiemap,
+        .llseek = smb3_llseek,
 };
 
 struct smb_version_operations smb21_operations = {
@@ -4266,6 +4351,7 @@ struct smb_version_operations smb21_operations = {
         .ioctl_query_info = smb2_ioctl_query_info,
         .make_node = smb2_make_node,
         .fiemap = smb3_fiemap,
+        .llseek = smb3_llseek,
 };
 
 struct smb_version_operations smb30_operations = {
@@ -4375,6 +4461,7 @@ struct smb_version_operations smb30_operations = {
         .ioctl_query_info = smb2_ioctl_query_info,
         .make_node = smb2_make_node,
         .fiemap = smb3_fiemap,
+        .llseek = smb3_llseek,
 };
 
 struct smb_version_operations smb311_operations = {
@@ -4485,6 +4572,7 @@ struct smb_version_operations smb311_operations = {
         .ioctl_query_info = smb2_ioctl_query_info,
         .make_node = smb2_make_node,
         .fiemap = smb3_fiemap,
+        .llseek = smb3_llseek,
 };
 
 struct smb_version_values smb20_values = {