Hi all, Here is a code snippet from e4defrag.c, can be located @ http://git.kernel.org/?p=fs/ext2/e2fsprogs.git;a=blob_plain;f=misc/e4defrag.c;hb=next /* * get_file_extents() - Get file's extent list. * * @fd: defrag target file's descriptor. * @ext_list_head: the head of the extent list. */ static int get_file_extents(int fd, struct fiemap_extent_list **ext_list_head) { __u32 i; int ret; int ext_buf_size, fie_buf_size; __u64 pos = 0; struct fiemap *fiemap_buf = NULL; struct fiemap_extent *ext_buf = NULL; struct fiemap_extent_list *ext_list = NULL; /* Convert units, in bytes. * Be careful : now, physical block number in extent is 48bit, * and the maximum blocksize for ext4 is 4K(12bit), * so there is no overflow, but in future it may be changed. */ /* Alloc space for fiemap */ ext_buf_size = EXTENT_MAX_COUNT * sizeof(struct fiemap_extent); fie_buf_size = sizeof(struct fiemap) + ext_buf_size; fiemap_buf = malloc(fie_buf_size); if (fiemap_buf == NULL) return -1; ext_buf = fiemap_buf->fm_extents; memset(fiemap_buf, 0, fie_buf_size); fiemap_buf->fm_length = FIEMAP_MAX_OFFSET; fiemap_buf->fm_flags |= FIEMAP_FLAG_SYNC; fiemap_buf->fm_extent_count = EXTENT_MAX_COUNT; do { fiemap_buf->fm_start = pos; memset(ext_buf, 0, ext_buf_size); ret = ioctl(fd, FS_IOC_FIEMAP, fiemap_buf); if (ret < 0) goto out; for (i = 0; i < fiemap_buf->fm_mapped_extents; i++) { ext_list = NULL; ext_list = malloc(sizeof(struct fiemap_extent_list)); if (ext_list == NULL) goto out; ext_list->data.physical = ext_buf[i].fe_physical / block_size; ext_list->data.logical = ext_buf[i].fe_logical / block_size; ext_list->data.len = ext_buf[i].fe_length / block_size; ret = insert_extent_by_physical( ext_list_head, ext_list); if (ret < 0) { FREE(ext_list); goto out; } } /* Record file's logical offset this time */ pos = ext_buf[EXTENT_MAX_COUNT-1].fe_logical + ext_buf[EXTENT_MAX_COUNT-1].fe_length; /* * If fm_extents array has been filled and * there are extents left, continue to cycle. */ } while (fiemap_buf->fm_mapped_extents == EXTENT_MAX_COUNT && !(ext_buf[EXTENT_MAX_COUNT-1].fe_flags & FIEMAP_EXTENT_LAST)); FREE(fiemap_buf); return 0; out: FREE(fiemap_buf); return -1; } Why do we have a while loop here, we have already made sure that we are initially itself allocating memory for EXTENT_MAX_COUNT? This is the maximum number of extents supported by the file system. Is this loop not redundant ? -- Regards, Sandeep. “To learn is to change. Education is a process that changes the learner.” -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
