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Subject[PATCH 2/5] sysctl: Add a new handler proc_show_minmax()
Date
The new handler will show the minimum and maximum values specified
in the extra1 and extra2 fields of the sysctl table entry.

Signed-off-by: Waiman Long <longman@redhat.com>
---
include/linux/sysctl.h | 2 ++
kernel/sysctl.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 93 insertions(+)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index bc09361..decb71e 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -63,6 +63,8 @@ extern int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int,
void __user *, size_t *, loff_t *);
extern int proc_do_large_bitmap(struct ctl_table *, int,
void __user *, size_t *, loff_t *);
+extern int proc_show_minmax(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos);

/*
* Register a set of sysctl names by calling register_sysctl_table
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 6c68e77..486126f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2700,6 +2700,97 @@ int proc_douintvec_minmax(struct ctl_table *table, int write,
do_proc_douintvec_minmax_conv, &param);
}

+/**
+ * proc_show_minmax - show the min/max values
+ * @table: the sysctl table
+ * @write: should always be %FALSE
+ * @buffer: the user buffer
+ * @lenp: the size of the user buffer
+ * @ppos: file position
+ *
+ * The table->data points to the original ctl_table which is used
+ * to determine the type of the min/max range as defined in the
+ * corresponding extra1 (min) and extra2 (max) field. The range
+ * will be displayed as "[min, max]".
+ *
+ * Returns 0 on success.
+ */
+int proc_show_minmax(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct ctl_table *ctbl = (struct ctl_table *)table->data;
+ unsigned long min, max;
+ bool min_neg, max_neg;
+ int err = 0;
+ size_t left;
+
+ if (write || !ctbl || ((ctbl->maxlen != sizeof(int)) &&
+ (ctbl->maxlen != sizeof(long))))
+ return -EINVAL;
+
+ if (*ppos) {
+ /* Not the first time */
+ *lenp = 0;
+ return 0;
+ }
+
+ min_neg = max_neg = false;
+ if (ctbl->proc_handler == proc_douintvec_minmax) {
+ min = ctbl->extra1 ? *(unsigned int *)ctbl->extra1 : 0;
+ max = ctbl->extra2 ? *(unsigned int *)ctbl->extra2 : UINT_MAX;
+ } else if (ctbl->maxlen == sizeof(int)) {
+ /* Assume to be signed integer */
+ unsigned int val;
+
+ val = ctbl->extra1 ? *(int *)ctbl->extra1 : -INT_MAX;
+ if (val < 0) {
+ min = -val;
+ min_neg = true;
+ } else {
+ min = val;
+ min_neg = false;
+ }
+ val = ctbl->extra2 ? *(int *)ctbl->extra2 : INT_MAX;
+ if (val < 0) {
+ max = -val;
+ max_neg = true;
+ } else {
+ max = val;
+ max_neg = false;
+ }
+ } else {
+ /* Assume to be unsigned long */
+ min = ctbl->extra1 ? *(unsigned long *)ctbl->extra1 : 0;
+ max = ctbl->extra2 ? *(unsigned long *)ctbl->extra2 : ULONG_MAX;
+ }
+
+ left = *lenp;
+
+ /*
+ * Error checks are done only for proc_put_long() and the
+ * last proc_put_char().
+ */
+ proc_put_char(&buffer, &left, '[');
+ err = proc_put_long(&buffer, &left, min, min_neg);
+ if (err)
+ goto out;
+
+ proc_put_char(&buffer, &left, ',');
+ proc_put_char(&buffer, &left, ' ');
+ err = proc_put_long(&buffer, &left, max, max_neg);
+ if (err)
+ goto out;
+
+ proc_put_char(&buffer, &left, ']');
+ err = proc_put_char(&buffer, &left, '\n');
+
+out:
+ *lenp -= left;
+ *ppos += *lenp;
+
+ return err;
+}
+
static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
unsigned int *valp,
int write, void *data)
--
1.8.3.1
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