[runtime] Update comment with link to Linux Kernel fix.

diff --git a/mono/metadata/w32file-unix.c b/mono/metadata/w32file-unix.c
index a9d0c7fd59b1d8eb450d87fe407a7695483b5a87..8c97b06cc8c9aaa91add0272f64f3ec381417f60 100644 (file)
--- a/mono/metadata/w32file-unix.c
+++ b/mono/metadata/w32file-unix.c
@@ -2545,9 +2545,13 @@ gboolean mono_w32file_delete(const gunichar2 *name)
        
        if (retval == -1) {
                /* On linux, calling unlink on an non-existing file in a read-only mount will fail with EROFS.
-               The expected behavior is for this function to return FALSE and not trigger an exception.
-               To work around this behavior, we stat the file on failure.
-               */
+                * The expected behavior is for this function to return FALSE and not trigger an exception.
+                * To work around this behavior, we stat the file on failure.
+                *
+                * This was supposedly fixed on kernel 3.0 [1] but we could reproduce it with Ubuntu 16.04 which has kernel 4.4.
+                * We can't remove this workaround until the early 2020's when most Android deviced will have a fix.
+                * [1] https://github.com/torvalds/linux/commit/50338b889dc504c69e0cb316ac92d1b9e51f3c8a
+                */
                if (errno == EROFS) {
                        MonoIOStat stat;
                        if (mono_w32file_get_attributes_ex (name, &stat)) //The file exists, so must be due the RO file system