2021-01-07 07:27:47

by Adrian Hunter

[permalink] [raw]
Subject: [PATCH V4] scsi: ufs-debugfs: Add error counters

People testing have a need to know how many errors might be occurring
over time. Add error counters and expose them via debugfs.

A module initcall is used to create a debugfs root directory for
ufshcd-related items. In the case that modules are built-in, then
initialization is done in link order, so move ufshcd-core to the top of
the Makefile.

Signed-off-by: Adrian Hunter <[email protected]>
Reviewed-by: Avri Altman <[email protected]>
Reviewed-by: Bean Huo <[email protected]>
---


Changes in V4:
Added Reviewed-by: Bean Huo <[email protected]>

Changes in V3:
Fixed link order to ensure correct initcall ordering when
modules are built-in.
Amended commit message accordingly.

Changes in V2:
Add missing '#include "ufs-debugfs.h"' in ufs-debugfs.c
Reported-by: kernel test robot <[email protected]>


drivers/scsi/ufs/Makefile | 13 +++++---
drivers/scsi/ufs/ufs-debugfs.c | 56 ++++++++++++++++++++++++++++++++++
drivers/scsi/ufs/ufs-debugfs.h | 22 +++++++++++++
drivers/scsi/ufs/ufshcd.c | 19 ++++++++++++
drivers/scsi/ufs/ufshcd.h | 5 +++
5 files changed, 111 insertions(+), 4 deletions(-)
create mode 100644 drivers/scsi/ufs/ufs-debugfs.c
create mode 100644 drivers/scsi/ufs/ufs-debugfs.h

diff --git a/drivers/scsi/ufs/Makefile b/drivers/scsi/ufs/Makefile
index 4679af1b564e..06f3a3fe4a44 100644
--- a/drivers/scsi/ufs/Makefile
+++ b/drivers/scsi/ufs/Makefile
@@ -1,5 +1,14 @@
# SPDX-License-Identifier: GPL-2.0
# UFSHCD makefile
+
+# The link order is important here. ufshcd-core must initialize
+# before vendor drivers.
+obj-$(CONFIG_SCSI_UFSHCD) += ufshcd-core.o
+ufshcd-core-y += ufshcd.o ufs-sysfs.o
+ufshcd-core-$(CONFIG_DEBUG_FS) += ufs-debugfs.o
+ufshcd-core-$(CONFIG_SCSI_UFS_BSG) += ufs_bsg.o
+ufshcd-core-$(CONFIG_SCSI_UFS_CRYPTO) += ufshcd-crypto.o
+
obj-$(CONFIG_SCSI_UFS_DWC_TC_PCI) += tc-dwc-g210-pci.o ufshcd-dwc.o tc-dwc-g210.o
obj-$(CONFIG_SCSI_UFS_DWC_TC_PLATFORM) += tc-dwc-g210-pltfrm.o ufshcd-dwc.o tc-dwc-g210.o
obj-$(CONFIG_SCSI_UFS_CDNS_PLATFORM) += cdns-pltfrm.o
@@ -7,10 +16,6 @@ obj-$(CONFIG_SCSI_UFS_QCOM) += ufs_qcom.o
ufs_qcom-y += ufs-qcom.o
ufs_qcom-$(CONFIG_SCSI_UFS_CRYPTO) += ufs-qcom-ice.o
obj-$(CONFIG_SCSI_UFS_EXYNOS) += ufs-exynos.o
-obj-$(CONFIG_SCSI_UFSHCD) += ufshcd-core.o
-ufshcd-core-y += ufshcd.o ufs-sysfs.o
-ufshcd-core-$(CONFIG_SCSI_UFS_BSG) += ufs_bsg.o
-ufshcd-core-$(CONFIG_SCSI_UFS_CRYPTO) += ufshcd-crypto.o
obj-$(CONFIG_SCSI_UFSHCD_PCI) += ufshcd-pci.o
obj-$(CONFIG_SCSI_UFSHCD_PLATFORM) += ufshcd-pltfrm.o
obj-$(CONFIG_SCSI_UFS_HISI) += ufs-hisi.o
diff --git a/drivers/scsi/ufs/ufs-debugfs.c b/drivers/scsi/ufs/ufs-debugfs.c
new file mode 100644
index 000000000000..dee98dc72d29
--- /dev/null
+++ b/drivers/scsi/ufs/ufs-debugfs.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2020 Intel Corporation
+
+#include <linux/debugfs.h>
+
+#include "ufs-debugfs.h"
+#include "ufshcd.h"
+
+static struct dentry *ufs_debugfs_root;
+
+void __init ufs_debugfs_init(void)
+{
+ ufs_debugfs_root = debugfs_create_dir("ufshcd", NULL);
+}
+
+void __exit ufs_debugfs_exit(void)
+{
+ debugfs_remove_recursive(ufs_debugfs_root);
+}
+
+static int ufs_debugfs_stats_show(struct seq_file *s, void *data)
+{
+ struct ufs_hba *hba = s->private;
+ struct ufs_event_hist *e = hba->ufs_stats.event;
+
+#define PRT(fmt, typ) \
+ seq_printf(s, fmt, e[UFS_EVT_ ## typ].cnt)
+
+ PRT("PHY Adapter Layer errors (except LINERESET): %llu\n", PA_ERR);
+ PRT("Data Link Layer errors: %llu\n", DL_ERR);
+ PRT("Network Layer errors: %llu\n", NL_ERR);
+ PRT("Transport Layer errors: %llu\n", TL_ERR);
+ PRT("Generic DME errors: %llu\n", DME_ERR);
+ PRT("Auto-hibernate errors: %llu\n", AUTO_HIBERN8_ERR);
+ PRT("IS Fatal errors (CEFES, SBFES, HCFES, DFES): %llu\n", FATAL_ERR);
+ PRT("DME Link Startup errors: %llu\n", LINK_STARTUP_FAIL);
+ PRT("PM Resume errors: %llu\n", RESUME_ERR);
+ PRT("PM Suspend errors : %llu\n", SUSPEND_ERR);
+ PRT("Logical Unit Resets: %llu\n", DEV_RESET);
+ PRT("Host Resets: %llu\n", HOST_RESET);
+ PRT("SCSI command aborts: %llu\n", ABORT);
+#undef PRT
+ return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(ufs_debugfs_stats);
+
+void ufs_debugfs_hba_init(struct ufs_hba *hba)
+{
+ hba->debugfs_root = debugfs_create_dir(dev_name(hba->dev), ufs_debugfs_root);
+ debugfs_create_file("stats", 0400, hba->debugfs_root, hba, &ufs_debugfs_stats_fops);
+}
+
+void ufs_debugfs_hba_exit(struct ufs_hba *hba)
+{
+ debugfs_remove_recursive(hba->debugfs_root);
+}
diff --git a/drivers/scsi/ufs/ufs-debugfs.h b/drivers/scsi/ufs/ufs-debugfs.h
new file mode 100644
index 000000000000..f35b39c4b4f5
--- /dev/null
+++ b/drivers/scsi/ufs/ufs-debugfs.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2020 Intel Corporation
+ */
+
+#ifndef __UFS_DEBUGFS_H__
+#define __UFS_DEBUGFS_H__
+
+struct ufs_hba;
+
+#ifdef CONFIG_DEBUG_FS
+void __init ufs_debugfs_init(void);
+void __exit ufs_debugfs_exit(void);
+void ufs_debugfs_hba_init(struct ufs_hba *hba);
+void ufs_debugfs_hba_exit(struct ufs_hba *hba);
+#else
+static inline void ufs_debugfs_init(void) {}
+static inline void ufs_debugfs_exit(void) {}
+static inline void ufs_debugfs_hba_init(struct ufs_hba *hba) {}
+static inline void ufs_debugfs_hba_exit(struct ufs_hba *hba) {}
+#endif
+
+#endif
diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index bedb822a40a3..47ea0afa3a35 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -20,6 +20,7 @@
#include "ufs_quirks.h"
#include "unipro.h"
#include "ufs-sysfs.h"
+#include "ufs-debugfs.h"
#include "ufs_bsg.h"
#include "ufshcd-crypto.h"
#include <asm/unaligned.h>
@@ -4543,6 +4544,7 @@ void ufshcd_update_evt_hist(struct ufs_hba *hba, u32 id, u32 val)
e = &hba->ufs_stats.event[id];
e->val[e->pos] = val;
e->tstamp[e->pos] = ktime_get();
+ e->cnt += 1;
e->pos = (e->pos + 1) % UFS_EVENT_HIST_LENGTH;

ufshcd_vops_event_notify(hba, id, &val);
@@ -8331,6 +8333,8 @@ static int ufshcd_hba_init(struct ufs_hba *hba)
if (err)
goto out_disable_vreg;

+ ufs_debugfs_hba_init(hba);
+
hba->is_powered = true;
goto out;

@@ -8347,6 +8351,7 @@ static int ufshcd_hba_init(struct ufs_hba *hba)
static void ufshcd_hba_exit(struct ufs_hba *hba)
{
if (hba->is_powered) {
+ ufs_debugfs_hba_exit(hba);
ufshcd_variant_hba_exit(hba);
ufshcd_setup_vreg(hba, false);
ufshcd_suspend_clkscaling(hba);
@@ -9434,6 +9439,20 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)
}
EXPORT_SYMBOL_GPL(ufshcd_init);

+static int __init ufshcd_core_init(void)
+{
+ ufs_debugfs_init();
+ return 0;
+}
+
+static void __exit ufshcd_core_exit(void)
+{
+ ufs_debugfs_exit();
+}
+
+module_init(ufshcd_core_init);
+module_exit(ufshcd_core_exit);
+
MODULE_AUTHOR("Santosh Yaragnavi <[email protected]>");
MODULE_AUTHOR("Vinayak Holikatti <[email protected]>");
MODULE_DESCRIPTION("Generic UFS host controller driver Core");
diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
index 85f9d0fbfbd9..3f7db69ebc82 100644
--- a/drivers/scsi/ufs/ufshcd.h
+++ b/drivers/scsi/ufs/ufshcd.h
@@ -445,11 +445,13 @@ struct ufs_clk_scaling {
* @pos: index to indicate cyclic buffer position
* @reg: cyclic buffer for registers value
* @tstamp: cyclic buffer for time stamp
+ * @cnt: error counter
*/
struct ufs_event_hist {
int pos;
u32 val[UFS_EVENT_HIST_LENGTH];
ktime_t tstamp[UFS_EVENT_HIST_LENGTH];
+ unsigned long long cnt;
};

/**
@@ -823,6 +825,9 @@ struct ufs_hba {
u32 crypto_cfg_register;
struct blk_keyslot_manager ksm;
#endif
+#ifdef CONFIG_DEBUG_FS
+ struct dentry *debugfs_root;
+#endif
};

/* Returns true if clocks can be gated. Otherwise false */
--
2.17.1


2021-01-07 07:34:10

by Can Guo

[permalink] [raw]
Subject: Re: [PATCH V4] scsi: ufs-debugfs: Add error counters

On 2021-01-07 15:25, Adrian Hunter wrote:
> People testing have a need to know how many errors might be occurring
> over time. Add error counters and expose them via debugfs.
>
> A module initcall is used to create a debugfs root directory for
> ufshcd-related items. In the case that modules are built-in, then
> initialization is done in link order, so move ufshcd-core to the top of
> the Makefile.
>
> Signed-off-by: Adrian Hunter <[email protected]>
> Reviewed-by: Avri Altman <[email protected]>
> Reviewed-by: Bean Huo <[email protected]>

Reviewed-by: Can Guo <[email protected]>

> ---
>
>
> Changes in V4:
> Added Reviewed-by: Bean Huo <[email protected]>
>
> Changes in V3:
> Fixed link order to ensure correct initcall ordering when
> modules are built-in.
> Amended commit message accordingly.
>
> Changes in V2:
> Add missing '#include "ufs-debugfs.h"' in ufs-debugfs.c
> Reported-by: kernel test robot <[email protected]>
>
>
> drivers/scsi/ufs/Makefile | 13 +++++---
> drivers/scsi/ufs/ufs-debugfs.c | 56 ++++++++++++++++++++++++++++++++++
> drivers/scsi/ufs/ufs-debugfs.h | 22 +++++++++++++
> drivers/scsi/ufs/ufshcd.c | 19 ++++++++++++
> drivers/scsi/ufs/ufshcd.h | 5 +++
> 5 files changed, 111 insertions(+), 4 deletions(-)
> create mode 100644 drivers/scsi/ufs/ufs-debugfs.c
> create mode 100644 drivers/scsi/ufs/ufs-debugfs.h
>
> diff --git a/drivers/scsi/ufs/Makefile b/drivers/scsi/ufs/Makefile
> index 4679af1b564e..06f3a3fe4a44 100644
> --- a/drivers/scsi/ufs/Makefile
> +++ b/drivers/scsi/ufs/Makefile
> @@ -1,5 +1,14 @@
> # SPDX-License-Identifier: GPL-2.0
> # UFSHCD makefile
> +
> +# The link order is important here. ufshcd-core must initialize
> +# before vendor drivers.
> +obj-$(CONFIG_SCSI_UFSHCD) += ufshcd-core.o
> +ufshcd-core-y += ufshcd.o ufs-sysfs.o
> +ufshcd-core-$(CONFIG_DEBUG_FS) += ufs-debugfs.o
> +ufshcd-core-$(CONFIG_SCSI_UFS_BSG) += ufs_bsg.o
> +ufshcd-core-$(CONFIG_SCSI_UFS_CRYPTO) += ufshcd-crypto.o
> +
> obj-$(CONFIG_SCSI_UFS_DWC_TC_PCI) += tc-dwc-g210-pci.o ufshcd-dwc.o
> tc-dwc-g210.o
> obj-$(CONFIG_SCSI_UFS_DWC_TC_PLATFORM) += tc-dwc-g210-pltfrm.o
> ufshcd-dwc.o tc-dwc-g210.o
> obj-$(CONFIG_SCSI_UFS_CDNS_PLATFORM) += cdns-pltfrm.o
> @@ -7,10 +16,6 @@ obj-$(CONFIG_SCSI_UFS_QCOM) += ufs_qcom.o
> ufs_qcom-y += ufs-qcom.o
> ufs_qcom-$(CONFIG_SCSI_UFS_CRYPTO) += ufs-qcom-ice.o
> obj-$(CONFIG_SCSI_UFS_EXYNOS) += ufs-exynos.o
> -obj-$(CONFIG_SCSI_UFSHCD) += ufshcd-core.o
> -ufshcd-core-y += ufshcd.o ufs-sysfs.o
> -ufshcd-core-$(CONFIG_SCSI_UFS_BSG) += ufs_bsg.o
> -ufshcd-core-$(CONFIG_SCSI_UFS_CRYPTO) += ufshcd-crypto.o
> obj-$(CONFIG_SCSI_UFSHCD_PCI) += ufshcd-pci.o
> obj-$(CONFIG_SCSI_UFSHCD_PLATFORM) += ufshcd-pltfrm.o
> obj-$(CONFIG_SCSI_UFS_HISI) += ufs-hisi.o
> diff --git a/drivers/scsi/ufs/ufs-debugfs.c
> b/drivers/scsi/ufs/ufs-debugfs.c
> new file mode 100644
> index 000000000000..dee98dc72d29
> --- /dev/null
> +++ b/drivers/scsi/ufs/ufs-debugfs.c
> @@ -0,0 +1,56 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2020 Intel Corporation
> +
> +#include <linux/debugfs.h>
> +
> +#include "ufs-debugfs.h"
> +#include "ufshcd.h"
> +
> +static struct dentry *ufs_debugfs_root;
> +
> +void __init ufs_debugfs_init(void)
> +{
> + ufs_debugfs_root = debugfs_create_dir("ufshcd", NULL);
> +}
> +
> +void __exit ufs_debugfs_exit(void)
> +{
> + debugfs_remove_recursive(ufs_debugfs_root);
> +}
> +
> +static int ufs_debugfs_stats_show(struct seq_file *s, void *data)
> +{
> + struct ufs_hba *hba = s->private;
> + struct ufs_event_hist *e = hba->ufs_stats.event;
> +
> +#define PRT(fmt, typ) \
> + seq_printf(s, fmt, e[UFS_EVT_ ## typ].cnt)
> +
> + PRT("PHY Adapter Layer errors (except LINERESET): %llu\n", PA_ERR);
> + PRT("Data Link Layer errors: %llu\n", DL_ERR);
> + PRT("Network Layer errors: %llu\n", NL_ERR);
> + PRT("Transport Layer errors: %llu\n", TL_ERR);
> + PRT("Generic DME errors: %llu\n", DME_ERR);
> + PRT("Auto-hibernate errors: %llu\n", AUTO_HIBERN8_ERR);
> + PRT("IS Fatal errors (CEFES, SBFES, HCFES, DFES): %llu\n",
> FATAL_ERR);
> + PRT("DME Link Startup errors: %llu\n", LINK_STARTUP_FAIL);
> + PRT("PM Resume errors: %llu\n", RESUME_ERR);
> + PRT("PM Suspend errors : %llu\n", SUSPEND_ERR);
> + PRT("Logical Unit Resets: %llu\n", DEV_RESET);
> + PRT("Host Resets: %llu\n", HOST_RESET);
> + PRT("SCSI command aborts: %llu\n", ABORT);
> +#undef PRT
> + return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(ufs_debugfs_stats);
> +
> +void ufs_debugfs_hba_init(struct ufs_hba *hba)
> +{
> + hba->debugfs_root = debugfs_create_dir(dev_name(hba->dev),
> ufs_debugfs_root);
> + debugfs_create_file("stats", 0400, hba->debugfs_root, hba,
> &ufs_debugfs_stats_fops);
> +}
> +
> +void ufs_debugfs_hba_exit(struct ufs_hba *hba)
> +{
> + debugfs_remove_recursive(hba->debugfs_root);
> +}
> diff --git a/drivers/scsi/ufs/ufs-debugfs.h
> b/drivers/scsi/ufs/ufs-debugfs.h
> new file mode 100644
> index 000000000000..f35b39c4b4f5
> --- /dev/null
> +++ b/drivers/scsi/ufs/ufs-debugfs.h
> @@ -0,0 +1,22 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2020 Intel Corporation
> + */
> +
> +#ifndef __UFS_DEBUGFS_H__
> +#define __UFS_DEBUGFS_H__
> +
> +struct ufs_hba;
> +
> +#ifdef CONFIG_DEBUG_FS
> +void __init ufs_debugfs_init(void);
> +void __exit ufs_debugfs_exit(void);
> +void ufs_debugfs_hba_init(struct ufs_hba *hba);
> +void ufs_debugfs_hba_exit(struct ufs_hba *hba);
> +#else
> +static inline void ufs_debugfs_init(void) {}
> +static inline void ufs_debugfs_exit(void) {}
> +static inline void ufs_debugfs_hba_init(struct ufs_hba *hba) {}
> +static inline void ufs_debugfs_hba_exit(struct ufs_hba *hba) {}
> +#endif
> +
> +#endif
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index bedb822a40a3..47ea0afa3a35 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -20,6 +20,7 @@
> #include "ufs_quirks.h"
> #include "unipro.h"
> #include "ufs-sysfs.h"
> +#include "ufs-debugfs.h"
> #include "ufs_bsg.h"
> #include "ufshcd-crypto.h"
> #include <asm/unaligned.h>
> @@ -4543,6 +4544,7 @@ void ufshcd_update_evt_hist(struct ufs_hba *hba,
> u32 id, u32 val)
> e = &hba->ufs_stats.event[id];
> e->val[e->pos] = val;
> e->tstamp[e->pos] = ktime_get();
> + e->cnt += 1;
> e->pos = (e->pos + 1) % UFS_EVENT_HIST_LENGTH;
>
> ufshcd_vops_event_notify(hba, id, &val);
> @@ -8331,6 +8333,8 @@ static int ufshcd_hba_init(struct ufs_hba *hba)
> if (err)
> goto out_disable_vreg;
>
> + ufs_debugfs_hba_init(hba);
> +
> hba->is_powered = true;
> goto out;
>
> @@ -8347,6 +8351,7 @@ static int ufshcd_hba_init(struct ufs_hba *hba)
> static void ufshcd_hba_exit(struct ufs_hba *hba)
> {
> if (hba->is_powered) {
> + ufs_debugfs_hba_exit(hba);
> ufshcd_variant_hba_exit(hba);
> ufshcd_setup_vreg(hba, false);
> ufshcd_suspend_clkscaling(hba);
> @@ -9434,6 +9439,20 @@ int ufshcd_init(struct ufs_hba *hba, void
> __iomem *mmio_base, unsigned int irq)
> }
> EXPORT_SYMBOL_GPL(ufshcd_init);
>
> +static int __init ufshcd_core_init(void)
> +{
> + ufs_debugfs_init();
> + return 0;
> +}
> +
> +static void __exit ufshcd_core_exit(void)
> +{
> + ufs_debugfs_exit();
> +}
> +
> +module_init(ufshcd_core_init);
> +module_exit(ufshcd_core_exit);
> +
> MODULE_AUTHOR("Santosh Yaragnavi <[email protected]>");
> MODULE_AUTHOR("Vinayak Holikatti <[email protected]>");
> MODULE_DESCRIPTION("Generic UFS host controller driver Core");
> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> index 85f9d0fbfbd9..3f7db69ebc82 100644
> --- a/drivers/scsi/ufs/ufshcd.h
> +++ b/drivers/scsi/ufs/ufshcd.h
> @@ -445,11 +445,13 @@ struct ufs_clk_scaling {
> * @pos: index to indicate cyclic buffer position
> * @reg: cyclic buffer for registers value
> * @tstamp: cyclic buffer for time stamp
> + * @cnt: error counter
> */
> struct ufs_event_hist {
> int pos;
> u32 val[UFS_EVENT_HIST_LENGTH];
> ktime_t tstamp[UFS_EVENT_HIST_LENGTH];
> + unsigned long long cnt;
> };
>
> /**
> @@ -823,6 +825,9 @@ struct ufs_hba {
> u32 crypto_cfg_register;
> struct blk_keyslot_manager ksm;
> #endif
> +#ifdef CONFIG_DEBUG_FS
> + struct dentry *debugfs_root;
> +#endif
> };
>
> /* Returns true if clocks can be gated. Otherwise false */

2021-01-08 03:50:19

by Martin K. Petersen

[permalink] [raw]
Subject: Re: [PATCH V4] scsi: ufs-debugfs: Add error counters


Adrian,

> People testing have a need to know how many errors might be occurring
> over time. Add error counters and expose them via debugfs.
>
> A module initcall is used to create a debugfs root directory for
> ufshcd-related items. In the case that modules are built-in, then
> initialization is done in link order, so move ufshcd-core to the top
> of the Makefile.

Applied to 5.12/scsi-staging, thanks!

--
Martin K. Petersen Oracle Linux Engineering

2021-01-15 05:48:34

by Martin K. Petersen

[permalink] [raw]
Subject: Re: [PATCH V4] scsi: ufs-debugfs: Add error counters

On Thu, 7 Jan 2021 09:25:38 +0200, Adrian Hunter wrote:

> People testing have a need to know how many errors might be occurring
> over time. Add error counters and expose them via debugfs.
>
> A module initcall is used to create a debugfs root directory for
> ufshcd-related items. In the case that modules are built-in, then
> initialization is done in link order, so move ufshcd-core to the top of
> the Makefile.

Applied to 5.12/scsi-queue, thanks!

[1/1] scsi: ufs-debugfs: Add error counters
https://git.kernel.org/mkp/scsi/c/b6cacaf2044f

--
Martin K. Petersen Oracle Linux Engineering