Hi Kumar, On Sat, Feb 26, 2022 at 9:18 PM Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote: > > On Sat, Feb 26, 2022 at 05:13:31AM IST, Hao Luo wrote: > > This patch allows bpf_syscall prog to perform some basic filesystem > > operations: create, remove directories and unlink files. Three bpf > > helpers are added for this purpose. When combined with the following > > patches that allow pinning and getting bpf objects from bpf prog, > > this feature can be used to create directory hierarchy in bpffs that > > help manage bpf objects purely using bpf progs. > > > > The added helpers subject to the same permission checks as their syscall > > version. For example, one can not write to a read-only file system; > > The identity of the current process is checked to see whether it has > > sufficient permission to perform the operations. > > > > Only directories and files in bpffs can be created or removed by these > > helpers. But it won't be too hard to allow these helpers to operate > > on files in other filesystems, if we want. > > > > Signed-off-by: Hao Luo <haoluo@xxxxxxxxxx> > > --- > > + * > > + * long bpf_mkdir(const char *pathname, int pathname_sz, u32 mode) > > + * Description > > + * Attempts to create a directory name *pathname*. The argument > > + * *pathname_sz* specifies the length of the string *pathname*. > > + * The argument *mode* specifies the mode for the new directory. It > > + * is modified by the process's umask. It has the same semantic as > > + * the syscall mkdir(2). > > + * Return > > + * 0 on success, or a negative error in case of failure. > > + * > > + * long bpf_rmdir(const char *pathname, int pathname_sz) > > + * Description > > + * Deletes a directory, which must be empty. > > + * Return > > + * 0 on sucess, or a negative error in case of failure. > > + * > > + * long bpf_unlink(const char *pathname, int pathname_sz) > > + * Description > > + * Deletes a name and possibly the file it refers to. It has the > > + * same semantic as the syscall unlink(2). > > + * Return > > + * 0 on success, or a negative error in case of failure. > > */ > > > > How about only introducing bpf_sys_mkdirat and bpf_sys_unlinkat? That would be > more useful for other cases in future, and when AT_FDCWD is passed, has the same > functionality as these, but when openat/fget is supported, it would work > relative to other dirfds as well. It can also allow using dirfd of the process > calling read for a iterator (e.g. if it sets the fd number using skel->bss). > unlinkat's AT_REMOVEDIR flag also removes the need for a bpf_rmdir. > > WDYT? > The idea sounds good to me, more flexible. But I don't have a real use case for using the added 'dirfd' at this moment. For all the use cases I can think of, absolute paths will suffice, I think. Unless other reviewers have opposition, I will try switching to mkdirat and unlinkat in v2.
