Questions tagged [system-calls]
Questions concerning the details of how a program uses system calls to interact with the kernel API, what calls are available, how they work etc.
353 questions
2
votes
0
answers
31
views
Wrong attributes bitmask in READDIR requests on NFSv4.1
I'm struggling the following problem.
I have an NFS v4.1 mount, where I have a directory with a couple of thousands files. I'm trying to list their names and types. Even with a minimal example program ...
- 21
0
votes
0
answers
21
views
How to trace recvfrom and sendto syscall each time apache2/httpd handle incoming http request?
So, I decided to start learn about system call with strace and want to observe network-related system call on apache2 processes, here's how I attach it:
pidof -s apache2
pstree -sTp <pid-from-pidof&...
- 33
0
votes
1
answer
106
views
How to better understand and reverse-engineer system calls within processes given a specific example
I am very new to linux and as such would appreciate any pointers with respect to understanding system calls and having the ability, knowledge and tools to reverse-engineer their origin or their ...
- 1
0
votes
0
answers
26
views
BPF program attached to `getname` won't get called when calling the `renameat2` syscall
I'm fiddling with a BPF program that needs to attach to the two "getname" functions that are being called from the renameat2 syscall, defined in linux/fs/namei.c as:
SYSCALL_DEFINE5(...
1
vote
0
answers
23
views
Retrieving the process descriptor during syscall
In Linux, there is a per-process kernel stack that stores at the bottom of it (or top if the stack grows upwards) a small struct named thread_info, which in turn points to the task_struct of the ...
1
vote
2
answers
283
views
Is systemd the first process that runs in user mode in linux?
I know that switching from user mode to kernel mode occurs continuously via system calls. My question is if systemd is the exact point during the starting of a linux system where the first ...
- 11
0
votes
0
answers
493
views
Running find on NFS mount much slower on RHEL8 vs RHEl7
I'm in the process of replacing some RHEL7 NFS server/client systems with RHEL8 systems, performing the same functions.
On the RHEL8 NFS client, I noticed running a find command on the NFS mount, is ...
10
votes
1
answer
2k
views
What is the rationale for the change of syscall calling convention in new Linuxes?
Quoting from https://www.kernel.org/doc/Documentation/process/adding-syscalls.rst:
At least on 64-bit x86, it will be a hard requirement from v4.17
onwards to not call system call functions in the ...
- 29.5k
6
votes
1
answer
1k
views
Does mmap() update the page table after every page fault?
Based on my research on mmap(), I understand that mmap uses demand paging to copy in data to the kernel page cache only when the virtual memory address is touched, through page fault.
If we are ...
- 63
6
votes
1
answer
361
views
getdents() syscall appears to be returning different results within a container
I'm trying to read what type of file /dev/null is. If I use stat() it reports correctly that it's a character device.
If I use getdents(), it also reports that it's a character device - unless I run ...
- 63
0
votes
0
answers
115
views
How to "wake-up" user space threads from kernel?
Suppose you have a kernel device driver receiving data and a user space threads waiting for the data.
You want to avoid wasted cycles by having the user space thread block and wake-up once the kernel ...
- 183
2
votes
1
answer
1k
views
Linux syscalls: advantage of copy_file_range over sendfile?
I understand that classically, the Linux Kernel was conservative about adding new syscalls.
But, I've learned about the existence of copy_file_range, which seems to do the exact same thing as sendfile....
- 506
0
votes
1
answer
63
views
Synchronous syscalls and uninterruptible sleep
My application entered uninteruptible sleep. The process is stuck at linkat.
❯ sudo cat /proc/1308028/syscall
265 0xffffffffffffff9c 0x7fbd9f32a120 0xffffffffffffff9c 0x7fbd9f395930 0x400 ...
- 101
4
votes
1
answer
162
views
is stat(2) read-after-write consistent with write(2)?
man 2 write states:
POSIX requires that a read(2) that can be proved to occur after a write() has returned will return the new data. Note that not all filesystems are POSIX conforming.
In Linux, is ...
1
vote
1
answer
767
views
Where does the signal that causes EINTR come from?
I Understand that EINTR is an error which so-called interruptible system calls may return. My question is where does the signal that causes EINTR come from?
I faced this quite often when using fnctl ...
- 11