Don't use WAL on devices where it's not supported (#5162)

(i.e., truly ancient kernels and weird FS).

In which case, we use TRUNCATE, which might be a tad less terrible than
DELETE on said weird crap FS.

frontend/device/generic/device.lua

@@ -39,6 +39,7 @@ local Device = {
     hasBGRFrameBuffer = no,
     canToggleGSensor = no,
     canToggleMassStorage = no,
+    canUseWAL = yes, -- requires mmap'ed I/O on the target FS
 
     -- use these only as a last resort. We should abstract the functionality
     -- and have device dependent implementations in the corresponting

frontend/device/kindle/device.lua

@@ -237,6 +237,7 @@ local Kindle2 = Kindle:new{
     hasDPad = yes,
     canHWInvert = no,
     canUseCBB = no, -- 4bpp
+    canUseWAL = no, -- Kernel too old to support mmap'ed I/O on /mnt/us
 }
 
 local KindleDXG = Kindle:new{
@@ -246,6 +247,7 @@ local KindleDXG = Kindle:new{
     hasDPad = yes,
     canHWInvert = no,
     canUseCBB = no, -- 4bpp
+    canUseWAL = no, -- Kernel too old to support mmap'ed I/O on /mnt/us
 }
 
 local Kindle3 = Kindle:new{

plugins/coverbrowser.koplugin/bookinfomanager.lua

@@ -1,5 +1,6 @@
 local Blitbuffer = require("ffi/blitbuffer")
 local DataStorage = require("datastorage")
+local Device = require("device")
 local DocumentRegistry = require("document/documentregistry")
 local RenderImage = require("ui/renderimage")
 local SQ3 = require("lua-ljsqlite3/init")
@@ -138,8 +139,12 @@ end
 
 function BookInfoManager:createDB()
     local db_conn = SQ3.open(self.db_location)
-    -- Make it WAL
-    db_conn:exec("PRAGMA journal_mode=WAL;")
+    -- Make it WAL, if possible
+    if Device:canUseWAL() then
+        db_conn:exec("PRAGMA journal_mode=WAL;")
+    else
+        db_conn:exec("PRAGMA journal_mode=TRUNCATE;")
+    end
     -- Less error cases to check if we do it that way
     -- Create it (noop if already there)
     db_conn:exec(BOOKINFO_DB_SCHEMA)

plugins/statistics.koplugin/main.lua

@@ -1,6 +1,7 @@
 local BookStatusWidget = require("ui/widget/bookstatuswidget")
 local ConfirmBox = require("ui/widget/confirmbox")
 local DataStorage = require("datastorage")
+local Device = require("device")
 local DocSettings = require("docsettings")
 local InfoMessage = require("ui/widget/infomessage")
 local KeyValuePage = require("ui/widget/keyvaluepage")
@@ -294,8 +295,12 @@ function ReaderStatistics:partialMd5(file)
 end
 
 function ReaderStatistics:createDB(conn)
-    -- Make it WAL
-    conn:exec("PRAGMA journal_mode=WAL;")
+    -- Make it WAL, if possible
+    if Device:canUseWAL() then
+        conn:exec("PRAGMA journal_mode=WAL;")
+    else
+        conn:exec("PRAGMA journal_mode=TRUNCATE;")
+    end
     local sql_stmt = [[
         CREATE TABLE IF NOT EXISTS book
             (