Zheaoli opened a new pull request, #4053:
URL: https://github.com/apache/opendal/pull/4053
**This feature is an experimental feature**
USDT is a way to allow people to pre-define some static hooks. Those hooks
could be used to fetch some internal information when the process runs.
I will use this PR to describe the detailed behavior of the DTrace in the
OpenDAL.
When people enabled `layers-dtrace` feature and added the layer to their
code like the following code:
```rust
use anyhow::Result;
use opendal::services::Fs;
use opendal::Operator;
use opendal::layers::DTraceLayer;
#[tokio::main]
async fn main() -> Result<()> {
let mut builder = Fs::default();
builder.root("/tmp");
// `Accessor` provides the low level APIs, we will use `Operator`
normally.
let op: Operator = Operator::new(builder)?.layer(DTraceLayer{}).finish();
let path="/tmp/test.txt";
for _ in 1..100000{
let bs = vec![0; 64 * 1024 * 1024];
op.write(path, bs).await?;
op.read(path).await?;
}
Ok(())
}
```
Then we compile the code, and use `readelf -n ${target_binary}` to get the
binary detail, we will find some information like following below
```text
Displaying notes found in: .note.stapsdt
Owner Data size Description
stapsdt 0x00000039 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: create_dir_start
Location: 0x00000000000f8f05, Base: 0x0000000000000000, Semaphore:
0x00000000003649f8
Arguments: -8@%rax
stapsdt 0x00000037 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: create_dir_end
Location: 0x00000000000f9284, Base: 0x0000000000000000, Semaphore:
0x00000000003649fa
Arguments: -8@%rax
stapsdt 0x0000003c NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_list_start
Location: 0x00000000000f9487, Base: 0x0000000000000000, Semaphore:
0x0000000000364a28
Arguments: -8@%rax
stapsdt 0x0000003a NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_list_end
Location: 0x00000000000f9546, Base: 0x0000000000000000, Semaphore:
0x0000000000364a2a
Arguments: -8@%rax
stapsdt 0x0000003c NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_read_start
Location: 0x00000000000f9740, Base: 0x0000000000000000, Semaphore:
0x0000000000364a18
Arguments: -8@%rax
stapsdt 0x0000003a NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_read_end
Location: 0x00000000000f97fd, Base: 0x0000000000000000, Semaphore:
0x0000000000364a1a
Arguments: -8@%rax
stapsdt 0x0000003c NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_stat_start
Location: 0x00000000000f99f3, Base: 0x0000000000000000, Semaphore:
0x0000000000364a20
Arguments: -8@%rax
stapsdt 0x0000003a NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_stat_end
Location: 0x00000000000f9ab9, Base: 0x0000000000000000, Semaphore:
0x0000000000364a22
Arguments: -8@%rax
stapsdt 0x0000003d NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_write_start
Location: 0x00000000000f9cec, Base: 0x0000000000000000, Semaphore:
0x0000000000364a1c
Arguments: -8@%rax
stapsdt 0x0000003b NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_write_end
Location: 0x00000000000f9df2, Base: 0x0000000000000000, Semaphore:
0x0000000000364a1e
Arguments: -8@%rax
stapsdt 0x0000003e NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_delete_start
Location: 0x00000000000f9fdc, Base: 0x0000000000000000, Semaphore:
0x0000000000364a24
Arguments: -8@%rax
stapsdt 0x0000003c NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_delete_end
Location: 0x00000000000fa0e6, Base: 0x0000000000000000, Semaphore:
0x0000000000364a26
Arguments: -8@%rax
stapsdt 0x00000042 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_create_dir_start
Location: 0x00000000000fa250, Base: 0x0000000000000000, Semaphore:
0x0000000000364a14
Arguments: -8@%rax
stapsdt 0x00000040 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: blocking_create_dir_end
Location: 0x00000000000fa30c, Base: 0x0000000000000000, Semaphore:
0x0000000000364a16
Arguments: -8@%rax
stapsdt 0x00000033 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: list_start
Location: 0x00000000000fa869, Base: 0x0000000000000000, Semaphore:
0x0000000000364a0c
Arguments: -8@%rax
stapsdt 0x00000031 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: list_end
Location: 0x00000000000faac7, Base: 0x0000000000000000, Semaphore:
0x0000000000364a0e
Arguments: -8@%rax
stapsdt 0x00000033 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: read_start
Location: 0x00000000000fb0a4, Base: 0x0000000000000000, Semaphore:
0x00000000003649fc
Arguments: -8@%rax
stapsdt 0x00000031 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: read_end
Location: 0x00000000000fb321, Base: 0x0000000000000000, Semaphore:
0x00000000003649fe
Arguments: -8@%rax
stapsdt 0x00000033 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: stat_start
Location: 0x00000000000fb8eb, Base: 0x0000000000000000, Semaphore:
0x0000000000364a04
Arguments: -8@%rax
stapsdt 0x00000031 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: stat_end
Location: 0x00000000000fbb66, Base: 0x0000000000000000, Semaphore:
0x0000000000364a06
Arguments: -8@%rax
stapsdt 0x00000034 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: write_start
Location: 0x00000000000fc6e5, Base: 0x0000000000000000, Semaphore:
0x0000000000364a00
Arguments: -8@%rax
stapsdt 0x00000032 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: write_end
Location: 0x00000000000fc954, Base: 0x0000000000000000, Semaphore:
0x0000000000364a02
Arguments: -8@%rax
stapsdt 0x00000035 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: delete_start
Location: 0x00000000000fcf30, Base: 0x0000000000000000, Semaphore:
0x0000000000364a08
Arguments: -8@%rax
stapsdt 0x00000033 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: delete_end
Location: 0x00000000000fd2aa, Base: 0x0000000000000000, Semaphore:
0x0000000000364a0a
Arguments: -8@%rax
stapsdt 0x00000036 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: presign_start
Location: 0x00000000000fd87b, Base: 0x0000000000000000, Semaphore:
0x0000000000364a10
Arguments: -8@%rax
stapsdt 0x00000034 NT_STAPSDT (SystemTap probe
descriptors)
Provider: opendal
Name: presign_end
Location: 0x00000000000fdaf6, Base: 0x0000000000000000, Semaphore:
0x0000000000364a12
Arguments: -8@%rax
```
We describe the offset, the argument of hook, and so many information else
in each section of the text. For example, the `write_start` hook, we can find
the offset is `0x00000000000fc6e5` and we can use gdb to verify it.
We will figure out the asm in 0x5555556506e5 is `NOP` (the process virtual
address started at 0x555555554000 on my machine, and
0x555555554000+0x00000000000fc6e5=0x5555556506e5). The `NOP` instruction code
will be replaced by the interrupt code when the hook is attached (In x86_64,
the interrupt code is INT3)
We can also set a breakpoint at this address.
We will find the code paused on line 146 in dtrace.rs. This is exactly what
we want
The USDT can help us debug it more easily and make it easier to trace it.
```text
╭─ manjusaka@manjusaka-garuda ~/Documents/projects/rust-demo
02:14:06
╰─ sudo bpftrace -e '
usdt:/home/manjusaka/Documents/projects/rust-demo/target/debug/demo:opendal:write_start
{
@start[tid,str(arg0)]=nsecs;
}
usdt:/home/manjusaka/Documents/projects/rust-demo/target/debug/demo:opendal:write_end
{
printf("Write %s use %d nsecs\n", str(arg0), nsecs -
@start[tid,str(arg0)]);
delete(@start[tid,str(arg0)]);
}' -p 385697
Attaching 2 probes...
Write tmp/test.txt use 59609 nsecs
Write tmp/test.txt use 56546 nsecs
Write tmp/test.txt use 53352 nsecs
Write tmp/test.txt use 57003 nsecs
Write tmp/test.txt use 58479 nsecs
Write tmp/test.txt use 52876 nsecs
Write tmp/test.txt use 56553 nsecs
Write tmp/test.txt use 59414 nsecs
Write tmp/test.txt use 101736 nsecs
Write tmp/test.txt use 54204 nsecs
Write tmp/test.txt use 63272 nsecs
Write tmp/test.txt use 64367 nsecs
Write tmp/test.txt use 56620 nsecs
Write tmp/test.txt use 56536 nsecs
Write tmp/test.txt use 55383 nsecs
Write tmp/test.txt use 52547 nsecs
Write tmp/test.txt use 50337 nsecs
Write tmp/test.txt use 52908 nsecs
Write tmp/test.txt use 59654 nsecs
Write tmp/test.txt use 64653 nsecs
Write tmp/test.txt use 66440 nsecs
```
We can use many other tools to trace it.
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