Re: [PATCH 1/2] libmtd: add `mtd_dev_present()' library function

[Artem Bityutskiy <dedekind1@gmail.com>]

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On Thu, 2012-02-02 at 14:20 +0100, Brian Foster wrote:
> On Thursday 02 February 2012 12:33:24 Artem Bityutskiy wrote:
> > On Fri, 2012-01-27 at 10:30 -0800, Brian Norris wrote:
> > > +int mtd_dev_present(libmtd_t desc, int mtd_num) {  [ ... ]
> > 
> > This will only work for relatively newer kernels where MTD has sysfs
> > support (2.6.30+). Older kernels have no MTD sysfs support and the sysfs
> > file you are stat()'ing won't exist, so this function will always return
> > an error.
> 
>  This is a very plausible concern:  Our older system
>  is mostly deployed with 2.6.26(or even older) kernel,
>  albeit a 2.6.30 option exists.  It has multiple MTD
>  devices, albeit due to the usage/configuration (and
>  maybe the use of older mtd-utils?) I suspect the bug
>  has never been observed.
> 
>  Our latest system uses 2.6.36, and is where the original
>  UBI-related bug was observed.

Ok, I've just prepared the below patch. Compile-tested only. Anyone
volunteers to verify?

From d3e5e0a2aeb61dbd99c41c11e1c268510a4334c2 Mon Sep 17 00:00:00 2001
From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Date: Fri, 3 Feb 2012 09:15:31 +0200
Subject: [PATCH] limbtd: implement mtd_dev_present for old kernels

Implement the 'legacy_dev_present()' function which will check whether an MTD
device is present by scanning the /proc/mtd file when the MTD subsystem does
not support sysfs (the case for pre-2.6.30 kernels).

This patch also moves the 'mtd_dev_present()' function to a slightly more
logical position.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
---
 lib/libmtd.c        |   25 ++++++++++++-------------
 lib/libmtd_int.h    |    1 +
 lib/libmtd_legacy.c |   25 +++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/lib/libmtd.c b/lib/libmtd.c
index 888d118..ecf182f 100644
--- a/lib/libmtd.c
+++ b/lib/libmtd.c
@@ -641,6 +641,18 @@ void libmtd_close(libmtd_t desc)
 	free(lib);
 }
 
+int mtd_dev_present(libmtd_t desc, int mtd_num) {
+	struct stat st;
+	struct libmtd *lib = (struct libmtd *)desc;
+	char file[strlen(lib->mtd) + 10];
+
+	if (!lib->sysfs_supported)
+		return legacy_dev_present(mtd_num);
+
+	sprintf(file, lib->mtd, mtd_num);
+	return !stat(file, &st);
+}
+
 int mtd_get_info(libmtd_t desc, struct mtd_info *info)
 {
 	DIR *sysfs_mtd;
@@ -713,19 +725,6 @@ out_close:
 	return -1;
 }
 
-int mtd_dev_present(libmtd_t desc, int mtd_num) {
-	struct stat st;
-	struct libmtd *lib = (struct libmtd *)desc;
-	char file[strlen(lib->mtd) + 10];
-
-	if (!lib->sysfs_supported)
-		/* TODO: add legacy_dev_present() function */
-		return 1;
-
-	sprintf(file, lib->mtd, mtd_num);
-	return !stat(file, &st);
-}
-
 int mtd_get_dev_info1(libmtd_t desc, int mtd_num, struct mtd_dev_info *mtd)
 {
 	int ret;
diff --git a/lib/libmtd_int.h b/lib/libmtd_int.h
index bb48d35..7913e67 100644
--- a/lib/libmtd_int.h
+++ b/lib/libmtd_int.h
@@ -95,6 +95,7 @@ struct libmtd
 };
 
 int legacy_libmtd_open(void);
+int legacy_dev_present(int mtd_num);
 int legacy_mtd_get_info(struct mtd_info *info);
 int legacy_get_dev_info(const char *node, struct mtd_dev_info *mtd);
 int legacy_get_dev_info1(int dev_num, struct mtd_dev_info *mtd);
diff --git a/lib/libmtd_legacy.c b/lib/libmtd_legacy.c
index d6c3938..d3f1672 100644
--- a/lib/libmtd_legacy.c
+++ b/lib/libmtd_legacy.c
@@ -170,6 +170,31 @@ int legacy_libmtd_open(void)
 }
 
 /**
+ * legacy_dev_presentl - legacy version of 'mtd_dev_present()'.
+ * @info: the MTD device information is returned here
+ *
+ * When the kernel does not provide sysfs files for the MTD subsystem,
+ * fall-back to parsing the /proc/mtd file to determine whether an mtd device
+ * number @mtd_num is present.
+ */
+int legacy_dev_present(int mtd_num)
+{
+	int ret;
+	struct proc_parse_info pi;
+
+	ret = proc_parse_start(&pi);
+	if (ret)
+		return -1;
+
+	while (proc_parse_next(&pi)) {
+		if (pi.mtd_num == mtd_num)
+			return 1;
+	}
+
+	return 0;
+}
+
+/**
  * legacy_mtd_get_info - legacy version of 'mtd_get_info()'.
  * @info: the MTD device information is returned here
  *
-- 
1.7.9



-- 
Best Regards,
Artem Bityutskiy


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