mmc: add module parameter to set whether cards are assumed removable

Some people run general-purpose distribution kernels on netbooks with
a card that is physically non-removable or logically non-removable
(e.g. used for /home) and cannot be cleanly unmounted during suspend.
Add a module parameter to set whether cards are assumed removable or
non-removable, with the default set by CONFIG_MMC_UNSAFE_RESUME.

In general, it is not possible to tell whether a card present in an MMC
slot after resume is the same that was there before suspend.  So there are
two possible behaviours, each of which will cause data loss in some cases:

CONFIG_MMC_UNSAFE_RESUME=n (default): Cards are assumed to be removed
during suspend.  Any filesystem on them must be unmounted before suspend;
otherwise, buffered writes will be lost.

CONFIG_MMC_UNSAFE_RESUME=y: Cards are assumed to remain present during
suspend.  They must not be swapped during suspend; otherwise, buffered
writes will be flushed to the wrong card.

Currently the choice is made at compile time and this allows that to be
overridden at module load time.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Wouter van Heyst <larstiq@larstiq.dyndns.org>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 7dab2e5..30acd52 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -48,6 +48,22 @@ int use_spi_crc = 1;
 module_param(use_spi_crc, bool, 0);
 
 /*
+ * We normally treat cards as removed during suspend if they are not
+ * known to be on a non-removable bus, to avoid the risk of writing
+ * back data to a different card after resume.  Allow this to be
+ * overridden if necessary.
+ */
+#ifdef CONFIG_MMC_UNSAFE_RESUME
+int mmc_assume_removable;
+#else
+int mmc_assume_removable = 1;
+#endif
+module_param_named(removable, mmc_assume_removable, bool, 0644);
+MODULE_PARM_DESC(
+	removable,
+	"MMC/SD cards are removable and may be removed during suspend");
+
+/*
  * Internal function. Schedule delayed work in the MMC work queue.
  */
 static int mmc_schedule_delayed_work(struct delayed_work *work,