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Subject[PATCH 1/1] sysfs: add more info to the oops dump
Date
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 1 > /sys/kernel/slab/:at-0000064/sanity_checks
$ echo c > /proc/sysrq-trigger
...
[ 112.457580] last sysfs file (w): /sys/kernel/slab/:at-0000064/sanity_checks
[ 112.464569] written: 1

Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com>
---
fs/sysfs/file.c | 21 ++++++++++++++++++++-
1 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index da3fefe..281e4dd 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -26,9 +26,18 @@

/* used in crash dumps to help with debugging */
static char last_sysfs_file[PATH_MAX];
+static char last_sysfs_write[16];
+static int last_sysfs_write_len; /* magic value < 0 => read */
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\n",
+ (last_sysfs_write_len < 0) ? 'r' : 'w',
+ last_sysfs_file);
+ if (last_sysfs_write_len >= sizeof(last_sysfs_write))
+ printk(KERN_EMERG " written: %s...(%d chars)\n",
+ last_sysfs_write, last_sysfs_write_len);
+ else if (last_sysfs_write_len > 0)
+ printk(KERN_EMERG " written: %s\n", last_sysfs_write);
}

/*
@@ -200,12 +209,19 @@ 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 +379,9 @@ 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 = -1; /* magic value */
}

/* File needs read support.
--
1.7.2.rc1.37.gf8c40


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