less on /proc files

[Corinna Vinschen via Cygwin-apps]

Hi Marco,

Achim made me aware yesterday, that less(1) shows nothing at all when
called on files under /proc.

Turns out, this only works on Linux, because there's a Linux-specific
kludge in less, checking if a file of size 0 is on the /proc filesystem
and if so, handles it accordingly.

Unfortunately the Linux kludge won't work for Cygwin without adding new
stuff to Cygwin:

- A <linux/magic.h> file, which sounds a bit weird, and 

- adding real f_type info to statfs().

This would make less on /proc files only work starting with Cygwin 3.6,
but there's another, simpler solution working with all recent Cygwin
versions. I created a small patch to less, doing a simple path check
and then handling /proc files just as in the Linux-specific code:

--- origsrc/less-643/ch.c       2023-07-21 00:43:12.000000000 +0200
+++ src/less-643/ch.c   2024-08-05 22:37:03.103333500 +0200
@@ -719,6 +719,20 @@ public void ch_flush(void)
                        }
                }
        }
+#elif defined (__CYGWIN__)
+       if (ch_fsize == 0)
+       {
+               char proclink[PATH_MAX];
+               char filename[PATH_MAX];
+               snprintf(proclink, sizeof proclink, "/proc/%u/fd/%d",
+                        getpid(), ch_file);
+               if (readlink(proclink, filename, sizeof filename) > 6 &&
+                   strncmp (filename, "/proc/", 6) == 0)
+               {
+                               ch_fsize = NULL_POSITION;
+                               ch_flags &= ~CH_CANSEEK;
+               }
+       }
 #endif
 
        if (lseek(ch_file, (off_t)0, SEEK_SET) == BAD_LSEEK)

Would it be ok for you to push out a new less release with this or a
similar patch?


Thanks,
Corinna