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Kernel+LibC: Implement the openat() syscall

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POSIX's openat() is very similar to open(), except you also provide a
file descriptor referring to a directory from which relative paths
should be resolved.

Passing it the magical fd number AT_FDCWD means "resolve from current
directory" (which is indeed also what open() normally does.)

This fixes libarchive's bsdtar, since it was trying to do something
extremely wrong in the absence of openat() support. The issue has
recently been fixed upstream in libarchive:

https://github.com/libarchive/libarchive/issues/1239

However, we should have openat() support anyway, so I went ahead and
implemented it. :^)

Fixes #748.
This commit is contained in:
Andreas Kling 2019-11-10 13:47:02 +01:00
parent 4f27745136
commit 18348cebf1
6 changed files with 80 additions and 7 deletions
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3
Libraries/LibC/unistd.h
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@ -77,6 +77,9 @@ int creat(const char* path, mode_t);
int open(const char* path, int options, ...);
int creat_with_path_length(const char* path, size_t path_length, mode_t);
int open_with_path_length(const char* path, size_t path_length, int options, mode_t);
#define AT_FDCWD -100
int openat(int dirfd, const char* path, int options, ...);
int openat_with_path_length(int dirfd, const char* path, size_t path_length, int options, mode_t);
ssize_t read(int fd, void* buf, size_t count);
ssize_t write(int fd, const void* buf, size_t count);
int close(int fd);