[PATCH] mtd: keep original flags for every struct mtd_info

[Boris Brezillon]

On Tue, 20 Nov 2018 10:43:38 +0100

On Tue, 20 Nov 2018 09:55:45 +0100

When allocating a new partition mtd subsystem runs internal tests in
the
allocate_partition(). They may result in modifying specified flags
(e.g.
dropping some /features/ like write access).
Those constraints don't have to be necessary true for subpartitions.
It
may happen parent partition isn't block aligned (effectively disabling
write access) while subpartition may fit blocks nicely. In such case
all
checks should be run again (starting with original flags value).
---
drivers/mtd/mtdcore.c | 2 ++
drivers/mtd/mtdpart.c | 3 ++-
include/linux/mtd/mtd.h | 1 +
3 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 97ac219c082e..2d24701255e5 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -665,6 +665,8 @@ static void mtd_set_dev_defaults(struct mtd_info
*mtd)
} else {
pr_debug("mtd device won't show a device symlink in sysfs\n");
}
+
+ mtd->orig_flags = mtd->flags;
}
/**
diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
index 99c460facd5e..2b6e53af47da 100644
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -346,7 +346,8 @@ static struct mtd_part *allocate_partition(struct
mtd_info *parent,
/* set up the MTD object for this partition */
slave->mtd.type = parent->type;
- slave->mtd.flags = parent->flags & ~part->mask_flags;
+ slave->mtd.flags = parent->orig_flags & ~part->mask_flags;
+ slave->mtd.orig_flags = slave->mtd.flags;
slave->mtd.size = part->size;
slave->mtd.writesize = parent->writesize;
slave->mtd.writebufsize = parent->writebufsize;
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index cd0be91bdefa..b491a08e87e5 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -207,6 +207,7 @@ struct mtd_debug_info {
struct mtd_info {
u_char type;
uint32_t flags;
+ uint32_t orig_flags; /* Flags as before running mtd checks */

Hm, I'm not a big fan of this orig_flags field. I'd prefer to have
Miquel's patch series [1] ported to Linus, so that master can be
struct mtd_info *mtd_get_master(struct mtd_info *mtd)
{
struct mtd_info *master = mtd;
while (master->parent)
master = master->parent;
}

Retrieving master is not a big deal, but I don't think it's going to
help. Just because master is writeable doesn't mean every subpartition
should be.
Let me try to provide some example covering both cases.
. "spi0.0" orig_flags:MTD_WRITEABLE flags:MTD_WRITEABLE
├── "boot" orig_flags:0 flags:0
├── "firmware" orig_flags:MTD_WRITEABLE flags:0 (misaligned partition)
├── "header" flags: ? (misaligned partition)
├── "rootfs" flags: ? (aligned partition)
└── "kernel" flags: ? (aligned partition)
└── "calibration" flags:0
├── "wifi0" flags: ?
└── "wifi1" flags: ?
My patch is intended to fix "rootfs" and "kernel" not having
MTD_WRITEABLE flag. The reason for lacking flag is mtd subsystem
(correctly) dropping it in the allocate_partition() due to misalignment.
If we start checking flags of the master however that will result in
"wifi0" and "wifi1" receiving MTD_WRITEABLE. The intention of
"calibration" was to make all calibration data (unit specific thing) RO
only.

I see.

I don't have any better idea than "orig_flags" that would help solving
this problem :(

Me neither. I just misunderstood what you were trying to do.

[Boris Brezillon]

On Tue, 20 Nov 2018 09:55:45 +0100

When allocating a new partition mtd subsystem runs internal tests in the
allocate_partition(). They may result in modifying specified flags (e.g.
dropping some /features/ like write access).
Those constraints don't have to be necessary true for subpartitions. It
may happen parent partition isn't block aligned (effectively disabling
write access) while subpartition may fit blocks nicely. In such case all
checks should be run again (starting with original flags value).

Queued to mtd/next.

Thanks,

Boris

---
drivers/mtd/mtdcore.c | 2 ++
drivers/mtd/mtdpart.c | 3 ++-
include/linux/mtd/mtd.h | 1 +
3 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 97ac219c082e..2d24701255e5 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -665,6 +665,8 @@ static void mtd_set_dev_defaults(struct mtd_info *mtd)
} else {
pr_debug("mtd device won't show a device symlink in sysfs\n");
}
+
+ mtd->orig_flags = mtd->flags;
}
/**
diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
index 99c460facd5e..2b6e53af47da 100644
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -346,7 +346,8 @@ static struct mtd_part *allocate_partition(struct mtd_info *parent,
/* set up the MTD object for this partition */
slave->mtd.type = parent->type;
- slave->mtd.flags = parent->flags & ~part->mask_flags;
+ slave->mtd.flags = parent->orig_flags & ~part->mask_flags;
+ slave->mtd.orig_flags = slave->mtd.flags;
slave->mtd.size = part->size;
slave->mtd.writesize = parent->writesize;
slave->mtd.writebufsize = parent->writebufsize;
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index cd0be91bdefa..b491a08e87e5 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -207,6 +207,7 @@ struct mtd_debug_info {
struct mtd_info {
u_char type;
uint32_t flags;
+ uint32_t orig_flags; /* Flags as before running mtd checks */
uint64_t size; // Total size of the MTD
/* "Major" erase size for the device. Naïve users may take this