Make /proc/self/fd `work'.

On Linux, /proc/<pid>/fd is comparable to fdescfs, where it allows you
to inspect the file descriptors used by each process. Glibc's ttyname()
works by performing a readlink() on these nodes, since all nodes in this
directory are symlinks.

It is a bit hard to implement this in linprocfs right now, so I am not
going to bother. Add a way to make ttyname(3) work, by adding a
/proc/<pid>/fd symlink, which points to /dev/fd only if the calling
process matches. When fdescfs is mounted, this will cause the
readlink() in ttyname() to fail, causing it to fall back on manually
finding a matching node in /dev.

Discussed on:	emulation@

1 files changed, 16 insertions, 0 deletions

diff --git a/sys/compat/linprocfs/linprocfs.c b/sys/compat/linprocfs/linprocfs.c
index 541db2f..ba08fd2 100644
--- a/sys/compat/linprocfs/linprocfs.c
+++ b/sys/compat/linprocfs/linprocfs.c
@@ -1245,6 +1245,20 @@ linprocfs_domodules(PFS_FILL_ARGS)
 #endif
 
 /*
+ * Filler function for proc/pid/fd
+ */
+static int
+linprocfs_dofdescfs(PFS_FILL_ARGS)
+{
+
+	if (p == curproc)
+		sbuf_printf(sb, "/dev/fd");
+	else
+		sbuf_printf(sb, "unknown");
+	return (0);
+}
+
+/*
  * Constructor
  */
 static int
@@ -1312,6 +1326,8 @@ linprocfs_init(PFS_INIT_ARGS)
 	    NULL, NULL, NULL, PFS_RD);
 	pfs_create_file(dir, "status", &linprocfs_doprocstatus,
 	    NULL, NULL, NULL, PFS_RD);
+	pfs_create_link(dir, "fd", &linprocfs_dofdescfs,
+	    NULL, NULL, NULL, 0);
 
 	/* /proc/scsi/... */
 	dir = pfs_create_dir(root, "scsi", NULL, NULL, NULL, 0);