Is it safe to parse a /proc/ file?

Question

I want to parse /proc/net/tcp/, but is it safe?

How should I open and read files from /proc/ and not be afraid, that some other process (o

Answer 1

When you read from a /proc file, the kernel is calling a function which has been registered in advance to be the "read" function for that proc file. See the __proc_file_read function in fs/proc/generic.c .

Therefore, the safety of the proc read is only as safe as the function the kernel calls to satisfy the read request. If that function properly locks all data it touches and returns to you in a buffer, then it is completely safe to read using that function. Since proc files like the one used for satisfying read requests to /proc/net/tcp have been around for a while and have undergone scrupulous review, they are about as safe as you could ask for. In fact, many common Linux utilities rely on reading from the proc filesystem and formatting the output in a different way. (Off the top of my head, I think 'ps' and 'netstat' do this).

As always, you don't have to take my word for it; you can look at the source to calm your fears. The following documentation from proc_net_tcp.txt tells you where the "read" functions for /proc/net/tcp live, so you can look at the actual code that is run when you read from that proc file and verify for yourself that there are no locking hazards.

This document describes the interfaces /proc/net/tcp and /proc/net/tcp6.
Note that these interfaces are deprecated in favor of tcp_diag. These /proc interfaces provide information about currently active TCP connections, and are implemented by tcp4_seq_show() in net/ipv4/tcp_ipv4.c and tcp6_seq_show() in net/ipv6/tcp_ipv6.c, respectively.