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authorLuke Shumaker <lukeshu@parabola.nu>2012-11-25 20:05:09 -0500
committerLuke Shumaker <lukeshu@lukeshu.com>2017-03-25 12:09:40 -0400
commitbaf8ae6d8d185c980aca65e0ae772a0ad5d2fb61 (patch)
tree04807f33567e3c25253af7ead5813e840655fbc9
parentd149cc9baf581e234cdf357ce37a604bf73115ea (diff)
lib/common.sh: lock, slock: Allow locks to be inherited.
Allow for locks to be inherited. Inheriting the lock is something that mkarchroot could do previously, but has since lost the ability to do. This allows for the programs to be more compos-able. Do this by instead of unconditionally opening $file on $fd, first check if $file is already open on $fd; and go ahead use it if it is. The naive way of doing this would be to `$(readlink /dev/fd/$fd)` and compare that to `$file`. However, if `$file` is itself a symlink; or there is a symlink somewhere in the path to `$file`, then this could easily fail. Instead, check `[[ "/dev/fd/$fd" -ef "$file" ]]`. Even though the Bash documentation (`help test`) says that `-ef` checks for if the two files are hard links to eachother, because it uses stat(3) (which resolves symlinks) to do this check, it also works with the /dev/fd/ soft links.
-rw-r--r--lib/common.sh12
1 files changed, 10 insertions, 2 deletions
diff --git a/lib/common.sh b/lib/common.sh
index 689772f..63b7795 100644
--- a/lib/common.sh
+++ b/lib/common.sh
@@ -138,7 +138,11 @@ get_full_version() {
# usage : lock( $fd, $file, $message )
##
lock() {
- eval "exec $1>"'"$2"'
+ # Only reopen the FD if it wasn't handed to us
+ if ! [[ "/dev/fd/$1" -ef "$2" ]]; then
+ eval "exec $1>"'"$2"'
+ fi
+
if ! flock -n $1; then
stat_busy "$3"
flock $1
@@ -150,7 +154,11 @@ lock() {
# usage : slock( $fd, $file, $message )
##
slock() {
- eval "exec $1>"'"$2"'
+ # Only reopen the FD if it wasn't handed to us
+ if ! [[ "/dev/fd/$1" -ef "$2" ]]; then
+ eval "exec $1>"'"$2"'
+ fi
+
if ! flock -sn $1; then
stat_busy "$3"
flock -s $1