Thank you for the comment. On Wed, 20 Mar 2019 12:05:25 -0700, Andrew Morton <[email protected]> wrote: > On Wed, 20 Mar 2019 18:29:29 +0900 Masatake YAMATO <[email protected]> wrote: > >> Finding endpoints of an IPC channel is one of essential task to >> understand how a user program works. Procfs and netlink socket provide >> enough hints to find endpoints for IPC channels like pipes, unix >> sockets, and pseudo terminals. However, there is no simple way to find >> endpoints for an eventfd file from userland. An inode number doesn't >> hint. Unlike pipe, all eventfd files share the same inode object. >> >> To provide the way to find endpoints of an eventfd file, this patch >> adds "eventfd-id" field to /proc/PID/fdinfo of eventfd as identifier. >> Address for eventfd context is used as id. >> >> A tool like lsof can utilize the information to print endpoints. >> >> ... >> >> --- a/fs/eventfd.c >> +++ b/fs/eventfd.c >> @@ -297,6 +297,7 @@ static void eventfd_show_fdinfo(struct seq_file *m, >> struct file *f) >> seq_printf(m, "eventfd-count: %16llx\n", >> (unsigned long long)ctx->count); >> spin_unlock_irq(&ctx->wqh.lock); >> + seq_printf(m, "eventfd-id: %p\n", ctx); >> } >> #endif > > Is it a good idea to use a bare kernel address for this? How does this > interact with printk pointer randomization and hashing? >
My understanding is that an address printed with %p for a bare kernel address is stable after ptr_key in vsprintf.c is filled, and ptr_key is filled enough early stage. so, for my usecase, resolving IPC endpoints, printing a bare kernel address with %p may be enough. Am I missing something? For the same purpose, I submitted a ida based patch a year ago. (https://patchwork.kernel.org/patch/10413589/) I quote it here for getting comments: This one doesn't use any bare kernel addresses. I implemented new one (%p version) bacause is is much shorter. Do you think ida based one is better than %p based one? Masatake YAMATO
