kernel/tools/perf/util/bpf-loader.h, branch linux-4.15.y

License cleanup: add SPDX GPL-2.0 license identifier to files with no license

2017-11-02T10:10:55Z

Many source files in the tree are missing licensing information, which makes it harder for compliance tools to determine the correct license. By default all files without license information are under the default license of the kernel, which is GPL version 2. Update the files which contain no license information with the 'GPL-2.0' SPDX license identifier. The SPDX identifier is a legally binding shorthand, which can be used instead of the full boiler plate text. This patch is based on work done by Thomas Gleixner and Kate Stewart and Philippe Ombredanne. How this work was done: Patches were generated and checked against linux-4.14-rc6 for a subset of the use cases: - file had no licensing information it it. - file was a */uapi/* one with no licensing information in it, - file was a */uapi/* one with existing licensing information, Further patches will be generated in subsequent months to fix up cases where non-standard license headers were used, and references to license had to be inferred by heuristics based on keywords. The analysis to determine which SPDX License Identifier to be applied to a file was done in a spreadsheet of side by side results from of the output of two independent scanners (ScanCode & Windriver) producing SPDX tag:value files created by Philippe Ombredanne. Philippe prepared the base worksheet, and did an initial spot review of a few 1000 files. The 4.13 kernel was the starting point of the analysis with 60,537 files assessed. Kate Stewart did a file by file comparison of the scanner results in the spreadsheet to determine which SPDX license identifier(s) to be applied to the file. She confirmed any determination that was not immediately clear with lawyers working with the Linux Foundation. Criteria used to select files for SPDX license identifier tagging was: - Files considered eligible had to be source code files. - Make and config files were included as candidates if they contained >5 lines of source - File already had some variant of a license header in it (even if <5 lines). All documentation files were explicitly excluded. The following heuristics were used to determine which SPDX license identifiers to apply. - when both scanners couldn't find any license traces, file was considered to have no license information in it, and the top level COPYING file license applied. For non */uapi/* files that summary was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 11139 and resulted in the first patch in this series. If that file was a */uapi/* path one, it was "GPL-2.0 WITH Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 WITH Linux-syscall-note 930 and resulted in the second patch in this series. - if a file had some form of licensing information in it, and was one of the */uapi/* ones, it was denoted with the Linux-syscall-note if any GPL family license was found in the file or had no licensing in it (per prior point). Results summary: SPDX license identifier # files ---------------------------------------------------|------ GPL-2.0 WITH Linux-syscall-note 270 GPL-2.0+ WITH Linux-syscall-note 169 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17 LGPL-2.1+ WITH Linux-syscall-note 15 GPL-1.0+ WITH Linux-syscall-note 14 ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5 LGPL-2.0+ WITH Linux-syscall-note 4 LGPL-2.1 WITH Linux-syscall-note 3 ((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3 ((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1 and that resulted in the third patch in this series. - when the two scanners agreed on the detected license(s), that became the concluded license(s). - when there was disagreement between the two scanners (one detected a license but the other didn't, or they both detected different licenses) a manual inspection of the file occurred. - In most cases a manual inspection of the information in the file resulted in a clear resolution of the license that should apply (and which scanner probably needed to revisit its heuristics). - When it was not immediately clear, the license identifier was confirmed with lawyers working with the Linux Foundation. - If there was any question as to the appropriate license identifier, the file was flagged for further research and to be revisited later in time. In total, over 70 hours of logged manual review was done on the spreadsheet to determine the SPDX license identifiers to apply to the source files by Kate, Philippe, Thomas and, in some cases, confirmation by lawyers working with the Linux Foundation. Kate also obtained a third independent scan of the 4.13 code base from FOSSology, and compared selected files where the other two scanners disagreed against that SPDX file, to see if there was new insights. The Windriver scanner is based on an older version of FOSSology in part, so they are related. Thomas did random spot checks in about 500 files from the spreadsheets for the uapi headers and agreed with SPDX license identifier in the files he inspected. For the non-uapi files Thomas did random spot checks in about 15000 files. In initial set of patches against 4.14-rc6, 3 files were found to have copy/paste license identifier errors, and have been fixed to reflect the correct identifier. Additionally Philippe spent 10 hours this week doing a detailed manual inspection and review of the 12,461 patched files from the initial patch version early this week with: - a full scancode scan run, collecting the matched texts, detected license ids and scores - reviewing anything where there was a license detected (about 500+ files) to ensure that the applied SPDX license was correct - reviewing anything where there was no detection but the patch license was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied SPDX license was correct This produced a worksheet with 20 files needing minor correction. This worksheet was then exported into 3 different .csv files for the different types of files to be modified. These .csv files were then reviewed by Greg. Thomas wrote a script to parse the csv files and add the proper SPDX tag to the file, in the format that the file expected. This script was further refined by Greg based on the output to detect more types of files automatically and to distinguish between header and source .c files (which need different comment types.) Finally Greg ran the script using the .csv files to generate the patches. Reviewed-by: Kate Stewart Reviewed-by: Philippe Ombredanne Reviewed-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

perf tools: Include errno.h where needed

2017-04-19T16:01:51Z

Removing it from util.h, part of an effort to disentangle the includes hell, that makes changes to util.h or something included by it to cause a complete rebuild of the tools. Cc: Adrian Hunter Cc: David Ahern Cc: Jiri Olsa Cc: Namhyung Kim Cc: Wang Nan Link: http://lkml.kernel.org/n/tip-ztrjy52q1rqcchuy3rubfgt2@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo

perf bpf: Rename bpf__foreach_tev() to bpf__foreach_event()

2016-07-14T02:09:03Z

Following commit will allow BPF script attach to tracepoints. bpf__foreach_tev() will iterate over all events, not only kprobes. Rename it to bpf__foreach_event(). Since only group and event are used by caller, there's no need to pass full 'struct probe_trace_event' to bpf_prog_iter_callback_t. Pass only these two strings. After this patch bpf_prog_iter_callback_t natually support tracepoints. Signed-off-by: Wang Nan Cc: Alexei Starovoitov Cc: Jiri Olsa Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1468406646-21642-5-git-send-email-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo

perf bpf: Clone bpf stdout events in multiple bpf scripts

2016-04-12T01:17:45Z

This patch allows cloning bpf-output event configuration among multiple bpf scripts. If there exist a map named '__bpf_output__' and not configured using 'map:__bpf_output__.event=', this patch clones the configuration of another '__bpf_stdout__' map. For example, following command: # perf trace --ev bpf-output/no-inherit,name=evt/ \ --ev ./test_bpf_trace.c/map:__bpf_stdout__.event=evt/ \ --ev ./test_bpf_trace2.c usleep 100000 equals to: # perf trace --ev bpf-output/no-inherit,name=evt/ \ --ev ./test_bpf_trace.c/map:__bpf_stdout__.event=evt/ \ --ev ./test_bpf_trace2.c/map:__bpf_stdout__.event=evt/ \ usleep 100000 Signed-off-by: Wang Nan Suggested-by: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1460128045-97310-4-git-send-email-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo

perf tools: Support setting different slots in a BPF map separately

2016-02-22T15:48:50Z

This patch introduces basic facilities to support config different slots in a BPF map one by one. array.nr_ranges and array.ranges are introduced into 'struct parse_events_term', where ranges is an array of indices range (start, length) which will be configured by this config term. nr_ranges is the size of the array. The array is passed to 'struct bpf_map_priv'. To indicate the new type of configuration, BPF_MAP_KEY_RANGES is added as a new key type. bpf_map_config_foreach_key() is extended to iterate over those indices instead of all possible keys. Code in this commit will be enabled by following commit which enables the indices syntax for array configuration. Signed-off-by: Wang Nan Cc: Adrian Hunter Cc: Alexei Starovoitov Cc: Brendan Gregg Cc: Cody P Schafer Cc: He Kuang Cc: Jeremie Galarneau Cc: Jiri Olsa Cc: Kirill Smelkov Cc: Li Zefan Cc: Masami Hiramatsu Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1456132275-98875-8-git-send-email-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo

perf tools: Enable passing event to BPF object

2016-02-22T15:30:50Z

A new syntax is added to the parser so that the user can access predefined perf events in BPF objects. After this patch, BPF programs for perf are finally able to utilize bpf_perf_event_read() introduced in commit 35578d798400 ("bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU counter"). Test result: # cat test_bpf_map_2.c /************************ BEGIN **************************/ #include #define SEC(NAME) __attribute__((section(NAME), used)) struct bpf_map_def { unsigned int type; unsigned int key_size; unsigned int value_size; unsigned int max_entries; }; static int (*trace_printk)(const char *fmt, int fmt_size, ...) = (void *)BPF_FUNC_trace_printk; static int (*get_smp_processor_id)(void) = (void *)BPF_FUNC_get_smp_processor_id; static int (*perf_event_read)(struct bpf_map_def *, int) = (void *)BPF_FUNC_perf_event_read; struct bpf_map_def SEC("maps") pmu_map = { .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY, .key_size = sizeof(int), .value_size = sizeof(int), .max_entries = __NR_CPUS__, }; SEC("func_write=sys_write") int func_write(void *ctx) { unsigned long long val; char fmt[] = "sys_write: pmu=%llu\n"; val = perf_event_read(&pmu_map, get_smp_processor_id()); trace_printk(fmt, sizeof(fmt), val); return 0; } SEC("func_write_return=sys_write%return") int func_write_return(void *ctx) { unsigned long long val = 0; char fmt[] = "sys_write_return: pmu=%llu\n"; val = perf_event_read(&pmu_map, get_smp_processor_id()); trace_printk(fmt, sizeof(fmt), val); return 0; } char _license[] SEC("license") = "GPL"; int _version SEC("version") = LINUX_VERSION_CODE; /************************* END ***************************/ Normal case: # echo "" > /sys/kernel/debug/tracing/trace # perf record -i -e cycles -e './test_bpf_map_2.c/map:pmu_map.event=cycles/' ls / [SNIP] [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.013 MB perf.data (7 samples) ] # cat /sys/kernel/debug/tracing/trace | grep ls ls-17066 [000] d... 938449.863301: : sys_write: pmu=1157327 ls-17066 [000] dN.. 938449.863342: : sys_write_return: pmu=1225218 ls-17066 [000] d... 938449.863349: : sys_write: pmu=1241922 ls-17066 [000] dN.. 938449.863369: : sys_write_return: pmu=1267445 Normal case (system wide): # echo "" > /sys/kernel/debug/tracing/trace # perf record -i -e cycles -e './test_bpf_map_2.c/map:pmu_map.event=cycles/' -a ^C[ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.811 MB perf.data (120 samples) ] # cat /sys/kernel/debug/tracing/trace | grep -v '18446744073709551594' | grep -v perf | head -n 20 [SNIP] # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | gmain-30828 [002] d... 2740551.068992: : sys_write: pmu=84373 gmain-30828 [002] d... 2740551.068992: : sys_write_return: pmu=87696 gmain-30828 [002] d... 2740551.068996: : sys_write: pmu=100658 gmain-30828 [002] d... 2740551.068997: : sys_write_return: pmu=102572 Error case 1: # perf record -e './test_bpf_map_2.c' ls / [SNIP] [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.014 MB perf.data ] # cat /sys/kernel/debug/tracing/trace | grep ls ls-17115 [007] d... 2724279.665625: : sys_write: pmu=18446744073709551614 ls-17115 [007] dN.. 2724279.665651: : sys_write_return: pmu=18446744073709551614 ls-17115 [007] d... 2724279.665658: : sys_write: pmu=18446744073709551614 ls-17115 [007] dN.. 2724279.665677: : sys_write_return: pmu=18446744073709551614 (18446744073709551614 is 0xfffffffffffffffe (-2)) Error case 2: # perf record -e cycles -e './test_bpf_map_2.c/map:pmu_map.event=evt/' -a event syntax error: '..ps:pmu_map.event=evt/' \___ Event not found for map setting Hint: Valid config terms: map:[].value=[value] map:[].event=[event] [SNIP] Error case 3: # ls /proc/2348/task/ 2348 2505 2506 2507 2508 # perf record -i -e cycles -e './test_bpf_map_2.c/map:pmu_map.event=cycles/' -p 2348 ERROR: Apply config to BPF failed: Cannot set event to BPF map in multi-thread tracing Error case 4: # perf record -e cycles -e './test_bpf_map_2.c/map:pmu_map.event=cycles/' ls / ERROR: Apply config to BPF failed: Doesn't support inherit event (Hint: use -i to turn off inherit) Error case 5: # perf record -i -e raw_syscalls:sys_enter -e './test_bpf_map_2.c/map:pmu_map.event=raw_syscalls:sys_enter/' ls ERROR: Apply config to BPF failed: Can only put raw, hardware and BPF output event into a BPF map Error case 6: # perf record -i -e './test_bpf_map_2.c/map:pmu_map.event=123/' ls / event syntax error: '.._map.event=123/' \___ Incorrect value type for map [SNIP] Signed-off-by: Wang Nan Acked-by: Jiri Olsa Tested-by: Arnaldo Carvalho de Melo Cc: Adrian Hunter Cc: Alexei Starovoitov Cc: Brendan Gregg Cc: Cody P Schafer Cc: He Kuang Cc: Jeremie Galarneau Cc: Kirill Smelkov Cc: Li Zefan Cc: Masami Hiramatsu Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1456132275-98875-7-git-send-email-wangnan0@huawei.com Signed-off-by: He Kuang Signed-off-by: Arnaldo Carvalho de Melo

perf record: Apply config to BPF objects before recording

2016-02-22T15:28:02Z

bpf__apply_obj_config() is introduced as the core API to apply object config options to all BPF objects. This patch also does the real work for setting values for BPF_MAP_TYPE_PERF_ARRAY maps by inserting value stored in map's private field into the BPF map. This patch is required because we are not always able to set all BPF config during parsing. Further patch will set events created by perf to BPF_MAP_TYPE_PERF_EVENT_ARRAY maps, which is not exist until perf_evsel__open(). bpf_map_foreach_key() is introduced to iterate over each key needs to be configured. This function would be extended to support more map types and different key settings. In perf record, before start recording, call bpf__apply_config() to turn on all BPF config options. Test result: # cat ./test_bpf_map_1.c /************************ BEGIN **************************/ #include #define SEC(NAME) __attribute__((section(NAME), used)) struct bpf_map_def { unsigned int type; unsigned int key_size; unsigned int value_size; unsigned int max_entries; }; static void *(*map_lookup_elem)(struct bpf_map_def *, void *) = (void *)BPF_FUNC_map_lookup_elem; static int (*trace_printk)(const char *fmt, int fmt_size, ...) = (void *)BPF_FUNC_trace_printk; struct bpf_map_def SEC("maps") channel = { .type = BPF_MAP_TYPE_ARRAY, .key_size = sizeof(int), .value_size = sizeof(int), .max_entries = 1, }; SEC("func=sys_nanosleep") int func(void *ctx) { int key = 0; char fmt[] = "%d\n"; int *pval = map_lookup_elem(&channel, &key); if (!pval) return 0; trace_printk(fmt, sizeof(fmt), *pval); return 0; } char _license[] SEC("license") = "GPL"; int _version SEC("version") = LINUX_VERSION_CODE; /************************* END ***************************/ # echo "" > /sys/kernel/debug/tracing/trace # ./perf record -e './test_bpf_map_1.c/map:channel.value=11/' usleep 10 [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.012 MB perf.data ] # cat /sys/kernel/debug/tracing/trace # tracer: nop # # entries-in-buffer/entries-written: 1/1 #P:8 [SNIP] # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | usleep-18593 [007] d... 2394714.395539: : 11 # ./perf record -e './test_bpf_map_1.c/map:channel.value=101/' usleep 10 [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.012 MB perf.data ] # cat /sys/kernel/debug/tracing/trace # tracer: nop # # entries-in-buffer/entries-written: 1/1 #P:8 [SNIP] # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | usleep-18593 [007] d... 2394714.395539: : 11 usleep-19000 [006] d... 2394831.057840: : 101 Signed-off-by: Wang Nan Tested-by: Arnaldo Carvalho de Melo Cc: Adrian Hunter Cc: Alexei Starovoitov Cc: Brendan Gregg Cc: Cody P Schafer Cc: He Kuang Cc: Jeremie Galarneau Cc: Jiri Olsa Cc: Kirill Smelkov Cc: Li Zefan Cc: Masami Hiramatsu Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1456132275-98875-6-git-send-email-wangnan0@huawei.com Signed-off-by: He Kuang Signed-off-by: Arnaldo Carvalho de Melo

perf bpf: Add API to set values to map entries in a bpf object

2016-02-22T15:17:48Z

bpf__config_obj() is introduced as a core API to config BPF object after loading. One configuration option of maps is introduced. After this patch BPF object can accept assignments like: map:my_map.value=1234 (map.my_map.value looks pretty. However, there's a small but hard to fix problem related to flex's greedy matching. Please see [1]. Choose ':' to avoid it in a simpler way.) This patch is more complex than the work it does because the consideration of extension. In designing BPF map configuration, the following things should be considered: 1. Array indices selection: perf should allow user setting different value for different slots in an array, with syntax like: map:my_map.value[0,3...6]=1234; 2. A map should be set by different config terms, each for a part of it. For example, set each slot to the pid of a thread; 3. Type of value: integer is not the only valid value type. A perf counter can also be put into a map after commit 35578d798400 ("bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU counter") 4. For a hash table, it should be possible to use a string or other value as a key; 5. It is possible that map configuration is unable to be setup during parsing. A perf counter is an example. Therefore, this patch does the following: 1. Instead of updating map element during parsing, this patch stores map config options in 'struct bpf_map_priv'. Following patches will apply those configs at an appropriate time; 2. Link map operations in a list so a map can have multiple config terms attached, so different parts can be configured separately; 3. Make 'struct bpf_map_priv' extensible so that the following patches can add new types of keys and operations; 4. Use bpf_obj_config__map_funcs array to support more map config options. Since the patch changing the event parser to parse BPF object config is relative large, I've put it in another commit. Code in this patch can be tested after applying the next patch. [1] http://lkml.kernel.org/g/564ED621.4050500@huawei.com Signed-off-by: Wang Nan Cc: Adrian Hunter Cc: Alexei Starovoitov Cc: Brendan Gregg Cc: Cody P Schafer Cc: He Kuang Cc: Jeremie Galarneau Cc: Jiri Olsa Cc: Kirill Smelkov Cc: Li Zefan Cc: Masami Hiramatsu Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1456132275-98875-4-git-send-email-wangnan0@huawei.com Signed-off-by: He Kuang [ Changes "maps:my_map.value" to "map:my_map.value", improved error messages ] Signed-off-by: Arnaldo Carvalho de Melo

perf bpf: Rename bpf config to program config

2015-11-28T01:00:46Z

Following patches are going to introduce BPF object level configuration to enable setting values into BPF maps. To avoid confusion, this patch renames existing 'config' in bpf-loader.c to 'program config'. Following patches would introduce 'object config'. Signed-off-by: Wang Nan Cc: Alexei Starovoitov Cc: Masami Hiramatsu Cc: Namhyung Kim Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1448614067-197576-4-git-send-email-wangnan0@huawei.com Signed-off-by: Arnaldo Carvalho de Melo

perf bpf: Add prologue for BPF programs for fetching arguments

2015-11-18T20:51:04Z

This patch generates a prologue for a BPF program which fetches arguments for it. With this patch, the program can have arguments as follow: SEC("lock_page=__lock_page page->flags") int lock_page(struct pt_regs *ctx, int err, unsigned long flags) { return 1; } This patch passes at most 3 arguments from r3, r4 and r5. r1 is still the ctx pointer. r2 is used to indicate if dereferencing was done successfully. This patch uses r6 to hold ctx (struct pt_regs) and r7 to hold stack pointer for result. Result of each arguments first store on stack: low address BPF_REG_FP - 24 ARG3 BPF_REG_FP - 16 ARG2 BPF_REG_FP - 8 ARG1 BPF_REG_FP high address Then loaded into r3, r4 and r5. The output prologue for offn(...off2(off1(reg)))) should be: r6 <- r1 // save ctx into a callee saved register r7 <- fp r7 <- r7 - stack_offset // pointer to result slot /* load r3 with the offset in pt_regs of 'reg' */ (r7) <- r3 // make slot valid r3 <- r3 + off1 // prepare to read unsafe pointer r2 <- 8 r1 <- r7 // result put onto stack call probe_read // read unsafe pointer jnei r0, 0, err // error checking r3 <- (r7) // read result r3 <- r3 + off2 // prepare to read unsafe pointer r2 <- 8 r1 <- r7 call probe_read jnei r0, 0, err ... /* load r2, r3, r4 from stack */ goto success err: r2 <- 1 /* load r3, r4, r5 with 0 */ goto usercode success: r2 <- 0 usercode: r1 <- r6 // restore ctx // original user code If all of arguments reside in register (dereferencing is not required), gen_prologue_fastpath() will be used to create fast prologue: r3 <- (r1 + offset of reg1) r4 <- (r1 + offset of reg2) r5 <- (r1 + offset of reg3) r2 <- 0 P.S. eBPF calling convention is defined as: * r0 - return value from in-kernel function, and exit value for eBPF program * r1 - r5 - arguments from eBPF program to in-kernel function * r6 - r9 - callee saved registers that in-kernel function will preserve * r10 - read-only frame pointer to access stack Committer note: At least testing if it builds and loads: # cat test_probe_arg.c struct pt_regs; __attribute__((section("lock_page=__lock_page page->flags"), used)) int func(struct pt_regs *ctx, int err, unsigned long flags) { return 1; } char _license[] __attribute__((section("license"), used)) = "GPL"; int _version __attribute__((section("version"), used)) = 0x40300; # perf record -e ./test_probe_arg.c usleep 1 [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.016 MB perf.data ] # perf evlist perf_bpf_probe:lock_page # Signed-off-by: He Kuang Tested-by: Arnaldo Carvalho de Melo Cc: Alexei Starovoitov Cc: Masami Hiramatsu Cc: Wang Nan Cc: Zefan Li Cc: pi3orama@163.com Link: http://lkml.kernel.org/r/1447675815-166222-11-git-send-email-wangnan0@huawei.com Signed-off-by: Wang Nan Signed-off-by: Arnaldo Carvalho de Melo