Env: Linux Kernel 5.3; FS: ext4
When requesting stat(const char *pathname, struct stat *statbuf) how is the const char *pathname is checked for existence?
It is necessary since in case there is no such path stat returns -1 (ENOENT). Here is the program I was testing:
static const char *pathname = "/some/fancy/path/name";int main(void){ struct stat statbuf; unsigned long i = 0; int fd = -1; while(1){ if((++i) % 2){ fd = open(pathname, O_CREAT, 0644); } stat(pathname, &statbuf); if(i % 2){ close(fd); unlink(pathname); } }}Every 2 iterations the file was deleted and re-created again on the next one. To inspect kernel call stack I used perf report:
The call stack does not meet my expectation. I expected ext4 calls under the vfs_statx in order to traverse ext4 internal data structures which would probably require disk I/O.
If it was cached in the inode or dentry cache how to flush it in order to inspect what ext4 calls would require stat(const char *pathname, struct stat *statbuf);?
UPD: Taking closer look at the implementation I found that it seems to be taken from dentry cache as specified in the link_path_walk
