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Message-ID: <AM6PR03MB5080C17BB893CE931E40DA28993D2@AM6PR03MB5080.eurprd03.prod.outlook.com> Date: Tue, 10 Dec 2024 16:25:51 +0000 From: Juntong Deng <juntong.deng@...look.com> To: Christian Brauner <brauner@...nel.org> Cc: ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com, andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev, kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, memxor@...il.com, snorcht@...il.com, bpf@...r.kernel.org, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: [PATCH bpf-next v5 0/5] bpf: Add open-coded style process file iterator and bpf_fget_task() kfunc On 2024/12/10 14:44, Christian Brauner wrote: > On Tue, Dec 10, 2024 at 02:01:53PM +0000, Juntong Deng wrote: >> This patch series adds open-coded style process file iterator >> bpf_iter_task_file and bpf_fget_task() kfunc, and corresponding >> selftests test cases. >> >> In addition, since fs kfuncs is generic and useful for scenarios >> other than LSM, this patch makes fs kfuncs available for SYSCALL >> and TRACING program types [0]. >> >> [0]: https://lore.kernel.org/bpf/CAPhsuW6ud21v2xz8iSXf=CiDL+R_zpQ+p8isSTMTw=EiJQtRSw@mail.gmail.com/ >> >> Although iter/task_file already exists, for CRIB we still need the > > What is CRIB? > CRIB is Checkpoint/Restore In eBPF. Introductions to CRIB can be found at the following links: https://lpc.events/event/18/contributions/1812/ https://lore.kernel.org/bpf/AM6PR03MB58488045E4D0FA6AEDC8BDE099A52@AM6PR03MB5848.eurprd03.prod.outlook.com/T/#u https://lwn.net/Articles/984313/ >> open-coded iterator style process file iterator, and the same is true >> for other bpf iterators such as iter/tcp, iter/udp, etc. >> >> The traditional bpf iterator is more like a bpf version of procfs, but >> similar to procfs, it is not suitable for CRIB scenarios that need to >> obtain large amounts of complex, multi-level in-kernel information. >> >> The following is from previous discussions [2]. >> >> [2]: https://lore.kernel.org/bpf/AM6PR03MB5848CA34B5B68C90F210285E99B12@AM6PR03MB5848.eurprd03.prod.outlook.com/ >> >> This is because the context of bpf iterators is fixed and bpf iterators >> cannot be nested. This means that a bpf iterator program can only >> complete a specific small iterative dump task, and cannot dump >> multi-level data. >> >> An example, when we need to dump all the sockets of a process, we need >> to iterate over all the files (sockets) of the process, and iterate over >> the all packets in the queue of each socket, and iterate over all data >> in each packet. >> >> If we use bpf iterator, since the iterator can not be nested, we need to >> use socket iterator program to get all the basic information of all >> sockets (pass pid as filter), and then use packet iterator program to >> get the basic information of all packets of a specific socket (pass pid, >> fd as filter), and then use packet data iterator program to get all the >> data of a specific packet (pass pid, fd, packet index as filter). >> >> This would be complicated and require a lot of (each iteration) >> bpf program startup and exit (leading to poor performance). >> >> By comparison, open coded iterator is much more flexible, we can iterate >> in any context, at any time, and iteration can be nested, so we can >> achieve more flexible and more elegant dumping through open coded >> iterators. >> >> With open coded iterators, all of the above can be done in a single >> bpf program, and with nested iterators, everything becomes compact >> and simple. >> >> Also, bpf iterators transmit data to user space through seq_file, >> which involves a lot of open (bpf_iter_create), read, close syscalls, >> context switching, memory copying, and cannot achieve the performance >> of using ringbuf. >> >> Signed-off-by: Juntong Deng <juntong.deng@...look.com> >> --- >> v4 -> v5: >> * Add file type checks in test cases for process file iterator >> and bpf_fget_task(). >> >> * Use fentry to synchronize tests instead of waiting in a loop. >> >> * Remove path_d_path_kfunc_non_lsm test case. >> >> * Replace task_lookup_next_fdget_rcu() with fget_task_next(). >> >> * Remove future merge conflict section in cover letter (resolved). >> >> v3 -> v4: >> * Make all kfuncs generic, not CRIB specific. >> >> * Move bpf_fget_task to fs/bpf_fs_kfuncs.c. >> >> * Remove bpf_iter_task_file_get_fd and bpf_get_file_ops_type. >> >> * Use struct bpf_iter_task_file_item * as the return value of >> bpf_iter_task_file_next. >> >> * Change fd to unsigned int type and add next_fd. >> >> * Add KF_RCU_PROTECTED to bpf_iter_task_file_new. >> >> * Make fs kfuncs available to SYSCALL and TRACING program types. >> >> * Update all relevant test cases. >> >> * Remove the discussion section from cover letter. >> >> v2 -> v3: >> * Move task_file open-coded iterator to kernel/bpf/helpers.c. >> >> * Fix duplicate error code 7 in test_bpf_iter_task_file(). >> >> * Add comment for case when bpf_iter_task_file_get_fd() returns -1. >> >> * Add future plans in commit message of "Add struct file related >> CRIB kfuncs". >> >> * Add Discussion section to cover letter. >> >> v1 -> v2: >> * Fix a type definition error in the fd parameter of >> bpf_fget_task() at crib_common.h. >> >> Juntong Deng (5): >> bpf: Introduce task_file open-coded iterator kfuncs >> selftests/bpf: Add tests for open-coded style process file iterator >> bpf: Add bpf_fget_task() kfunc >> bpf: Make fs kfuncs available for SYSCALL and TRACING program types >> selftests/bpf: Add tests for bpf_fget_task() kfunc >> >> fs/bpf_fs_kfuncs.c | 42 ++++--- >> kernel/bpf/helpers.c | 3 + >> kernel/bpf/task_iter.c | 92 ++++++++++++++ >> .../testing/selftests/bpf/bpf_experimental.h | 15 +++ >> .../selftests/bpf/prog_tests/fs_kfuncs.c | 46 +++++++ >> .../testing/selftests/bpf/prog_tests/iters.c | 79 ++++++++++++ >> .../selftests/bpf/progs/fs_kfuncs_failure.c | 33 +++++ >> .../selftests/bpf/progs/iters_task_file.c | 88 ++++++++++++++ >> .../bpf/progs/iters_task_file_failure.c | 114 ++++++++++++++++++ >> .../selftests/bpf/progs/test_fget_task.c | 63 ++++++++++ >> .../selftests/bpf/progs/verifier_vfs_reject.c | 10 -- >> 11 files changed, 559 insertions(+), 26 deletions(-) >> create mode 100644 tools/testing/selftests/bpf/progs/fs_kfuncs_failure.c >> create mode 100644 tools/testing/selftests/bpf/progs/iters_task_file.c >> create mode 100644 tools/testing/selftests/bpf/progs/iters_task_file_failure.c >> create mode 100644 tools/testing/selftests/bpf/progs/test_fget_task.c >> >> -- >> 2.39.5 >>
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