sstate: Improve move into place op and touch file

Depending on the kernel and coreutils version, mv operations test for existence
of files and can potentially race. It also leads to the file always changing which
leads to potential problems if using and NFS share and there are other readers.

Using ln instead means we don't overwrite the file if it already exists meaning
other readers aren't disrupted and should work more reliably on NFS which is used
for sstate on the autobuilder.

Since we're not overwriting files, touch the file to show activity as would have
been done it it were reused from sstate.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

diff --git a/meta/classes/sstate.bbclass b/meta/classes/sstate.bbclass
index 356fe7ec180606b69ecd304b983bb66b5223f2eb..b4ffffcd98b4ae233e7091e60e08494bc973033a 100644 (file)
--- a/meta/classes/sstate.bbclass
+++ b/meta/classes/sstate.bbclass
@@ -776,6 +776,7 @@ sstate_task_postfunc[dirs] = "${WORKDIR}"
 sstate_create_package () {
        # Exit early if it already exists
        if [ -e ${SSTATE_PKG} ]; then
+               touch ${SSTATE_PKG}
                return
        fi
 
@@ -803,10 +804,13 @@ sstate_create_package () {
        chmod 0664 $TFILE
        # Skip if it was already created by some other process
        if [ ! -e ${SSTATE_PKG} ]; then
-               mv -f $TFILE ${SSTATE_PKG}
+               # Move into place using ln to attempt an atomic op.
+               # Abort if it already exists
+               ln $TFILE ${SSTATE_PKG} && rm $TFILE
        else
                rm $TFILE
        fi
+       touch ${SSTATE_PKG}
 }
 
 python sstate_sign_package () {