[PATCHv3 1/1] sysfs: add more info to the oops dump

[Phil Carmody]

If we're going to remember which file we accessed, we might as well
also remember whether it was a read or a write, and if the latter,
some indication of what was written.

e.g.
$ echo sesquipedalianism > /sys/module/vt/parameters/default_utf8
$ echo c > /proc/sysrq-trigger
...
[   57.522583] last sysfs file (w): /sys/module/vt/parameters/default_utf8  written: sesquipedaliani...(18 chars)

Signed-off-by: Phil Carmody <ext-phil.2.carmody@xxxxxxxxx>
---
 fs/sysfs/file.c |   24 +++++++++++++++++++++++-
 1 files changed, 23 insertions(+), 1 deletions(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index da3fefe..88ac53d 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -26,9 +26,21 @@
 
 /* used in crash dumps to help with debugging */
 static char last_sysfs_file[PATH_MAX];
+static char last_sysfs_write[16];
+/* To indicate the last operation was a read, use an impossible length */
+#define SYSFS_NOT_A_WRITE -1
+static int last_sysfs_write_len;
 void sysfs_printk_last_file(void)
 {
-	printk(KERN_EMERG "last sysfs file: %s\n", last_sysfs_file);
+	printk(KERN_EMERG "last sysfs file (%c): %s%c",
+	       (last_sysfs_write_len == SYSFS_NOT_A_WRITE) ? 'r' : 'w',
+	       last_sysfs_file,
+	       last_sysfs_write_len > 0 ? ' ' : '\n');
+	if (last_sysfs_write_len >= (int)sizeof(last_sysfs_write))
+		printk(KERN_CONT " written: %s...(%d chars)\n",
+		       last_sysfs_write, last_sysfs_write_len);
+	else if (last_sysfs_write_len > 0)
+		printk(KERN_CONT " written: %s\n", last_sysfs_write);
 }
 
 /*
@@ -200,12 +212,19 @@ flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t
 	struct sysfs_dirent *attr_sd = dentry->d_fsdata;
 	struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
 	const struct sysfs_ops * ops = buffer->ops;
+	int copylen = min(count, sizeof(last_sysfs_write) - 1);
 	int rc;
 
 	/* need attr_sd for attr and ops, its parent for kobj */
 	if (!sysfs_get_active(attr_sd))
 		return -ENODEV;
 
+	while (copylen > 0 && buffer->page[copylen-1] == '\n')
+		--copylen; /* never print trailing \n's */
+	memcpy(last_sysfs_write, buffer->page, copylen);
+	last_sysfs_write[copylen] = '\0';
+	last_sysfs_write_len = count;
+
 	rc = ops->store(kobj, attr_sd->s_attr.attr, buffer->page, count);
 
 	sysfs_put_active(attr_sd);
@@ -363,6 +382,9 @@ static int sysfs_open_file(struct inode *inode, struct file *file)
 	if (file->f_mode & FMODE_WRITE) {
 		if (!(inode->i_mode & S_IWUGO) || !ops->store)
 			goto err_out;
+		last_sysfs_write_len = 0;
+	} else {
+		last_sysfs_write_len = SYSFS_NOT_A_WRITE;
 	}
 
 	/* File needs read support.
-- 
1.7.2.rc1.37.gf8c40

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