lib-fs: fs-metawrap stat() and get_metadata(): use existing istream if possible

This may reduce reads from parent fs, but it's at least required for the
following commit.

diff --git a/src/lib-fs/fs-metawrap.c b/src/lib-fs/fs-metawrap.c
index a8c9f8ace520626418a2b04aa2c3d2321fa69b5d..ee187b96098a3d1d0ad35d4ee393221665bc4e60 100644 (file)
--- a/src/lib-fs/fs-metawrap.c
+++ b/src/lib-fs/fs-metawrap.c
@@ -199,14 +199,30 @@ fs_metawrap_get_metadata(struct fs_file *_file,
                         const ARRAY_TYPE(fs_metadata) **metadata_r)
 {
        struct metawrap_fs_file *file = (struct metawrap_fs_file *)_file;
+       ssize_t ret;
        char c;
 
        if (!file->fs->wrap_metadata)
                return fs_get_metadata(file->super, metadata_r);
 
-       if (!file->metadata_read) {
+       if (file->metadata_read) {
+               /* we have the metadata */
+       } else if (file->input == NULL) {
                if (fs_read(_file, &c, 1) < 0)
                        return -1;
+       } else {
+               /* use the existing istream to read it */
+               while ((ret = i_stream_read(file->input)) == 0) {
+                       if (file->metadata_read)
+                               break;
+
+                       i_assert(!file->input->blocking);
+                       if (fs_wait_async(_file->fs) < 0)
+                               return -1;
+               }
+               if (ret == -1)
+                       return -1;
+               i_assert(file->metadata_read);
        }
        *metadata_r = &_file->metadata;
        return 0;
@@ -469,7 +485,12 @@ static int fs_metawrap_stat(struct fs_file *_file, struct stat *st_r)
                return 0;
        }
 
-       input = fs_read_stream(_file, IO_BLOCK_SIZE);
+       if (file->input == NULL)
+               input = fs_read_stream(_file, IO_BLOCK_SIZE);
+       else {
+               input = file->input;
+               i_stream_ref(input);
+       }
        if ((ret = i_stream_get_size(input, TRUE, &input_size)) < 0) {
                fs_set_error(_file->fs, "i_stream_get_size(%s) failed: %s",
                             fs_file_path(_file), i_stream_get_error(input));