Author: delphij
Date: Sat Dec 14 09:54:30 2019
New Revision: 355749
URL: https://svnweb.freebsd.org/changeset/base/355749

Log:
  MFC r355247: Reduce disk write load in /usr/libexec/save-entropy.

Modified:
  stable/11/libexec/save-entropy/save-entropy.sh
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/libexec/save-entropy/save-entropy.sh
==============================================================================
--- stable/11/libexec/save-entropy/save-entropy.sh      Sat Dec 14 09:49:36 
2019        (r355748)
+++ stable/11/libexec/save-entropy/save-entropy.sh      Sat Dec 14 09:54:30 
2019        (r355749)
@@ -69,24 +69,61 @@ cd "${entropy_dir}" || {
 
 for f in saved-entropy.*; do
        case "${f}" in saved-entropy.\*) continue ;; esac       # No files match
-       [ ${f#saved-entropy\.} -ge ${entropy_save_num} ] && unlink ${f}
+       [ ${f#saved-entropy\.} -gt ${entropy_save_num} ] && unlink ${f}
 done
 
-umask 377
+umask 177
 
-n=$(( ${entropy_save_num} - 1 ))
-while [ ${n} -ge 1 ]; do
-       if [ -f "saved-entropy.${n}" ]; then
-               mv "saved-entropy.${n}" "saved-entropy.$(( ${n} + 1 ))"
-       elif [ -e "saved-entropy.${n}" -o -L "saved-entropy.${n}" ]; then
+# Scan slots [1..$entropy_save_num), picking an empty slot or the oldest
+# existing file if no empty slot was available.
+#
+# 1. Find out the first regular file or empty slot (and its serial number)
+#
+n=1
+while [ ${n} -le ${entropy_save_num} ]; do
+       save_file="saved-entropy.${n}"
+       if [ ! -e "${save_file}" -o -f "${save_file}" ]; then
+               break
+       else
                logger -is -t "$0" \
-       "${entropy_dir}/saved-entropy.${n}" is not a regular file, and so \
-           it will not be rotated. Entropy file rotation is aborted.
-               exit 1
+                   "${save_file}" is not a regular file, skipped.
        fi
-       n=$(( ${n} - 1 ))
+       n=$(( ${n} + 1 ))
 done
+#
+# 2. Start from (serial number + 1), and check if the slot is empty
+#    or is an older regular file, update save_file pointer in either
+#    case, and break early if we found an empty slot.
+#
+if [ -f ${save_file} ]; then
+       n=$(( ${n} + 1 ))
+       while [ ${n} -le ${entropy_save_num} ]; do
+               next_file=saved-entropy.${n}
+               if [ -f "${next_file}" ]; then
+                       [ "${next_file}" -ot "${save_file}" ] && \
+                           save_file="${next_file}"
+               elif [ ! -e "${next_file}" ]; then
+                       save_file="${next_file}"
+                       break
+               else
+                       logger -is -t "$0" \
+                           "${next_file}" is not a regular file, skipped.
+               fi
+               n=$(( ${n} + 1 ))
+       done
+fi
+#
+# 3. Check if the pointer we have in hand is really a regular file or
+#    an empty slot, and bail out as that means there is no available slot.
+#
+if [ -e "${save_file}" -a ! -f "${save_file}" ]; then
+       logger -is -t "$0" \
+               No available slot in "${entropy_dir}", save entropy is aborted.
+       exit 1
+fi
 
-dd if=/dev/random of=saved-entropy.1 bs=${entropy_save_sz} count=1 2>/dev/null
+# Save entropy to the selected slot.
+chmod 600 "${save_file}" 2>/dev/null || :
+dd if=/dev/random of="${save_file}" bs=${entropy_save_sz} count=1 2>/dev/null
 
 exit 0
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