system - write error: No space left on device in embedded linux -

all have embedded board, run linux os. , use yaffs2 rootfs. run program on it, after times, got error "error no space left on device.". checked flash, there still have lot free space. write config file. config file update. program write log flash. log size limited 2m. don't know why, , how solve. me please!(my first language not english,sorry. hope understand say)

some debug info:

    # ./write_test      version 1.0     close file :: no space left on device     return errno 28     # cat /proc/yaffs      yaffs built:nov 23 2015 16:57:34       device 0 "rootfs"     start_block........... 0     end_block............. 511     total_bytes_per_chunk. 2048     use_nand_ecc.......... 1     no_tags_ecc........... 1     is_yaffs2............. 1     inband_tags........... 0     empty_lost_n_found.... 0     disable_lazy_load..... 0     refresh_period........ 500     n_caches.............. 10     n_reserved_blocks..... 5     always_check_erased... 0     data_bytes_per_chunk.. 2048     chunk_grp_bits........ 0     chunk_grp_size........ 1     n_erased_blocks....... 366     blocks_in_checkpt..... 0      n_tnodes.............. 749     n_obj................. 477     n_free_chunks......... 23579      n_page_writes......... 6092     n_page_reads.......... 11524     n_erasures............ 96     n_gc_copies........... 5490     all_gcs............... 1136     passive_gc_count...... 1136     oldest_dirty_gc_count. 95     n_gc_blocks........... 96     bg_gcs................ 96     n_retired_writes...... 0     n_retired_blocks...... 0     n_ecc_fixed........... 0     n_ecc_unfixed......... 0     n_tags_ecc_fixed...... 0     n_tags_ecc_unfixed.... 0     cache_hits............ 0     n_deleted_files....... 0     n_unlinked_files...... 289     refresh_count......... 1     n_bg_deletions........ 0      device 2 "data"     start_block........... 0     end_block............. 927     total_bytes_per_chunk. 2048     use_nand_ecc.......... 1     no_tags_ecc........... 1     is_yaffs2............. 1     inband_tags........... 0     empty_lost_n_found.... 0     disable_lazy_load..... 0     refresh_period........ 500     n_caches.............. 10     n_reserved_blocks..... 5     always_check_erased... 0     data_bytes_per_chunk.. 2048     chunk_grp_bits........ 0     chunk_grp_size........ 1     n_erased_blocks....... 10     blocks_in_checkpt..... 0      n_tnodes.............. 4211     n_obj................. 24     n_free_chunks......... 658      n_page_writes......... 430     n_page_reads.......... 467     n_erasures............ 7     n_gc_copies........... 421     all_gcs............... 20     passive_gc_count...... 13     oldest_dirty_gc_count. 3     n_gc_blocks........... 6     bg_gcs................ 4     n_retired_writes...... 0     n_retired_blocks...... 0     n_ecc_fixed........... 0     n_ecc_unfixed......... 0     n_tags_ecc_fixed...... 0     n_tags_ecc_unfixed.... 0     cache_hits............ 0     n_deleted_files....... 0     n_unlinked_files...... 2     refresh_count......... 1     n_bg_deletions........ 0     #  

log , config file stored in "data". thanks!!

in general disk space (here flash), first of check flash space with df -h (or other commands have.. df present in busybox). if flash space (specially on program partition) ok, "inode" (directory) space problem, see inode usage df -i command.
(a link this: https://wiki.gentoo.org/wiki/knowledge_base:no_space_left_on_device_while_there_is_plenty_of_space_available)

if non of these problem cause, think have have deeper @ code, specially if deal disk i/o! mention aware of memory & heap space & free allocated spaces in functions.