Convert greybus/uart.c from IDR to XArray. The abstract data type XArray
is more memory-efficient, parallelisable, and cache friendly. It takes
advantage of RCU to perform lookups without locking. Furthermore, IDR is
deprecated because XArray has a better (cleaner and more consistent) API.
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx>
---
v3->v4:
Remove mutex_lock/unlock around xa_load(). These locks seem to
be unnecessary because there is a 1:1 correspondence between
a specific minor and its gb_tty and there is no reference
counting. I think that the RCU locks used inside xa_load()
are sufficient to protect this API from returning an invalid
gb_tty in case of concurrent access. Some more considerations
on this topic are in the following message to linux-kernel list:
https://lore.kernel.org/lkml/3554184.2JXonMZcNW@localhost.localdomain/
v2->v3:
Fix some issues according to a review by Alex Elder <elder@xxxxxxxx>
v1->v2:
Fix an issue found by the kernel test robot. It is due to
passing to xa_*lock() the same old mutex that IDR used with
the previous version of the code.
drivers/staging/greybus/uart.c | 32 ++++++++++++++------------------
1 file changed, 14 insertions(+), 18 deletions(-)
diff --git a/drivers/staging/greybus/uart.c b/drivers/staging/greybus/uart.c
index 73f01ed1e5b7..f66983adb51b 100644
--- a/drivers/staging/greybus/uart.c
+++ b/drivers/staging/greybus/uart.c
@@ -22,7 +22,7 @@
#include <linux/serial.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
-#include <linux/idr.h>
+#include <linux/xarray.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/kfifo.h>
@@ -32,8 +32,9 @@
#include "gbphy.h"
-#define GB_NUM_MINORS 16 /* 16 is more than enough */
-#define GB_NAME "ttyGB"
+#define GB_NUM_MINORS 16 /* 16 is more than enough */
+#define GB_RANGE_MINORS XA_LIMIT(0, GB_NUM_MINORS)
+#define GB_NAME "ttyGB"
#define GB_UART_WRITE_FIFO_SIZE PAGE_SIZE
#define GB_UART_WRITE_ROOM_MARGIN 1 /* leave some space in fifo */
@@ -67,8 +68,7 @@ struct gb_tty {
};
static struct tty_driver *gb_tty_driver;
-static DEFINE_IDR(tty_minors);
-static DEFINE_MUTEX(table_lock);
+static DEFINE_XARRAY(tty_minors);
static int gb_uart_receive_data_handler(struct gb_operation *op)
{
@@ -341,8 +341,7 @@ static struct gb_tty *get_gb_by_minor(unsigned int minor)
{
struct gb_tty *gb_tty;
- mutex_lock(&table_lock);
- gb_tty = idr_find(&tty_minors, minor);
+ gb_tty = xa_load(&tty_minors, minor);
if (gb_tty) {
mutex_lock(&gb_tty->mutex);
if (gb_tty->disconnected) {
@@ -353,19 +352,18 @@ static struct gb_tty *get_gb_by_minor(unsigned int minor)
mutex_unlock(&gb_tty->mutex);
}
}
- mutex_unlock(&table_lock);
return gb_tty;
}
static int alloc_minor(struct gb_tty *gb_tty)
{
int minor;
+ int ret;
- mutex_lock(&table_lock);
- minor = idr_alloc(&tty_minors, gb_tty, 0, GB_NUM_MINORS, GFP_KERNEL);
- mutex_unlock(&table_lock);
- if (minor >= 0)
- gb_tty->minor = minor;
+ ret = xa_alloc(&tty_minors, &minor, gb_tty, GB_RANGE_MINORS, GFP_KERNEL);
+ if (ret)
+ return ret;
+ gb_tty->minor = minor;
return minor;
}
@@ -374,9 +372,7 @@ static void release_minor(struct gb_tty *gb_tty)
int minor = gb_tty->minor;
gb_tty->minor = 0; /* Maybe should use an invalid value instead */
- mutex_lock(&table_lock);
- idr_remove(&tty_minors, minor);
- mutex_unlock(&table_lock);
+ xa_erase(&tty_minors, minor);
}
static int gb_tty_install(struct tty_driver *driver, struct tty_struct *tty)
@@ -837,7 +833,7 @@ static int gb_uart_probe(struct gbphy_device *gbphy_dev,
minor = alloc_minor(gb_tty);
if (minor < 0) {
- if (minor == -ENOSPC) {
+ if (minor == -EBUSY) {
dev_err(&gbphy_dev->dev,
"no more free minor numbers\n");
retval = -ENODEV;
@@ -982,7 +978,7 @@ static void gb_tty_exit(void)
{
tty_unregister_driver(gb_tty_driver);
put_tty_driver(gb_tty_driver);
- idr_destroy(&tty_minors);
+ xa_destroy(&tty_minors);
}
static const struct gbphy_device_id gb_uart_id_table[] = {
--
2.32.0
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