[bugfix] workaround if some SegmentMapping refers to end of tar

Currently it could happen on EROFS meta indexes.

Signed-off-by: Gao Xiang <[email protected]>

src/overlaybd/lsmt/file.cpp

@@ -573,9 +573,14 @@ class LSMTReadOnlyFile : public IFileRW {
  // LOG_DEBUG("offset: `, length: `", m.moffset, size);
  ssize_t ret = m_files[m.tag]->pread(buf, size, m.moffset * ALIGNMENT);
  if (ret < size) {
- LOG_ERRNO_RETURN(0, (int)ret,
- "failed to read from `-th file ( ` pread return: ` < size: `)",
- m.tag, m_files[m.tag], ret, size);
+ size_t ret2 = m_files[m.tag]->pread((char *)buf + ret, size - ret, m.moffset * ALIGNMENT + ret);
+ if (ret2) {
+ LOG_ERRNO_RETURN(0, (int)ret,
+ "failed to read from `-th file ( ` pread return: ` < size: `)",
+ m.tag, m_files[m.tag], ret, size);
+ } else {
+ memset((char *)buf + ret, 0, size - ret);
+ }
  }
  lsmt_io_size += ret;
  lsmt_io_cnt++;