feat(livenet): add memory size check depending on live image size

For writeable live images, the memory must hold the complete image.
That means it must be at least the size of the image plus some RAM
necessary to run processes.
With too small RAM, the OOM Killer steps in and makes the boot hang.
This patch lets the system go into the emergency shell instead.

The default minimum RAM after subtracting the live image size is set to 1G.
The parameter rd.minmem is added to modify this.

man/dracut.cmdline.7.asc

@@ -1126,6 +1126,13 @@ NOTE: There must be enough free RAM available to hold the complete image.
 +
 This method is very suitable for diskless boots.
 
+**rd.minmem=**__<megabyte>__::
+Specify minimum free RAM in MB after copying a live disk image into memory.
+The default is 1024.
++
+This parameter only applies together with the parameters rd.writable.fsimg
+or rd.live.ram.
+
 **root=**live:__<url>__::
 Boots a live image retrieved from __<url>__.  Requires the dracut 'livenet'
 module.  Valid handlers: __http, https, ftp, torrent, tftp__.

modules.d/90dmsquash-live/dmsquash-live-root.sh

@@ -315,6 +315,8 @@ if [ -e /run/initramfs/live/${live_dir}/${squash_image} ]; then
 fi
 if [ -e "$SQUASHED" ]; then
     if [ -n "$live_ram" ]; then
+        imgsize=$(($(stat -c %s -- $SQUASHED) / (1024 * 1024)))
+        check_live_ram $imgsize
         echo 'Copying live image to RAM...' > /dev/kmsg
         echo ' (this may take a minute)' > /dev/kmsg
         dd if=$SQUASHED of=/run/initramfs/squashed.img bs=512 2> /dev/null

modules.d/90livenet/livenetroot.sh

@@ -16,6 +16,13 @@ netroot="$2"
 liveurl="${netroot#livenet:}"
 info "fetching $liveurl"
 
+if getargbool 0 'rd.writable.fsimg'; then
+
+    imgsize=$(($(curl -sIL "$liveurl" | sed -n 's/Content-Length: *\([[:digit:]]*\).*/\1/p') / (1024 * 1024)))
+
+    check_live_ram $imgsize
+fi
+
 imgfile=
 #retry until the imgfile is populated with data or the max retries
 i=1

modules.d/99base/dracut-lib.sh

@@ -1151,3 +1151,28 @@ load_fstype() {
     done < /proc/filesystems
     modprobe "$1"
 }
+
+# parameter: size of live image
+# calls emergency shell if ram size is too small for the image
+check_live_ram() {
+    minmem=$(getarg rd.minmem)
+    minmem=${minmem:-1024}
+    imgsize=$1
+    memsize=$(($(sed -n 's/MemTotal: *\([[:digit:]]*\).*/\1/p' /proc/meminfo) / 1024))
+
+    if [ -z "$imgsize" ]; then
+        warn "Image size could not be determined"
+        return 0
+    fi
+
+    if [ $((memsize - imgsize)) -lt "$minmem" ]; then
+        sed -i "N;/and attach it to a bug report./s/echo$/echo\n\
+         echo \n\
+         echo 'Warning!!!'\n\
+         echo 'The memory size of your system is too small for this live image.'\n\
+         echo 'Expect killed processes due to out of memory conditions.'\n\
+         echo \n/" /usr/bin/dracut-emergency
+
+        emergency_shell
+    fi
+}