[PATCH v2] cooker: warn when sstate is outside of build dir, but hash equiv database is inside it

[Alexander Kanavin <alex.kanavin@gmail.com>]

From: Alexander Kanavin <alex@linutronix.de>

This should help with the long-standing usability problem: when
someone tweaks the configuration to put sstate somewhere else than
the default (so that it can be shared between local builds, or over NFS),
they should also share the hash equivalency database, but there would not
be any indication to do so.

This will issue a warning and recommend to start a dedicated hash equivalency
server (if sstate is on NFS), or set BB_HASHSERVE_DB_DIR (if it isn't).

Signed-off-by: Alexander Kanavin <alex@linutronix.de>

---
v2: guard against relevant variables not being defined
---
 lib/bb/cooker.py | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/lib/bb/cooker.py b/lib/bb/cooker.py
index 4b6ba3196..88be266bc 100644
--- a/lib/bb/cooker.py
+++ b/lib/bb/cooker.py
@@ -336,6 +336,25 @@ cannot be on a NFS mount due to potential NFS locking issues between sqlite clie
 If you need to share the database between several computers, set up a permanently running hash equivalency server
 according to https://docs.yoctoproject.org/dev-manual/hashequivserver.html""".format(bb_hashserve_db_dir))
                 dbdir = bb_hashserve_db_dir or self.data.getVar("PERSISTENT_DIR") or self.data.getVar("CACHE")
+
+                topdir = self.data.getVar("TOPDIR")
+                sstatedir = self.data.getVar("SSTATE_DIR")
+                if (dbdir and topdir and sstatedir and dbdir.startswith(topdir) and not sstatedir.startswith(topdir)):
+                    if utils.is_path_on_nfs(sstatedir):
+                        bb.warn("""Sstate directory is on a shared NFS (it is set via SSTATE_DIR to {}),
+but hash equivalency database is inside this particular build directory {}.
+
+This will prevent sstate reuse, and it is recommended to set up a permanently running hash equivalency server
+according to https://docs.yoctoproject.org/dev-manual/hashequivserver.html""".format(sstatedir, topdir))
+                    else:
+                        bb.warn("""Sstate directory is shared between several builds (it is set via SSTATE_DIR to {}),
+but hash equivalency database is inside this particular build directory {}.
+
+This will prevent sstate reuse, and it is recommended to set the location for the database to a common path
+via BB_HASHSERVE_DB_DIR, for example:
+
+BB_HASHSERVE_DB_DIR = \"${{SSTATE_DIR}}\"""".format(sstatedir, topdir))
+
                 os.makedirs(dbdir, exist_ok=True)
                 dbfile = dbdir + "/hashserv.db"
                 upstream = self.data.getVar("BB_HASHSERVE_UPSTREAM") or None
-- 
2.47.3