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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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20
Libraries/LibC/unistd.cpp
View file

@ -189,6 +189,17 @@ int open_with_path_length(const char* path, size_t path_length, int options, mod
__RETURN_WITH_ERRNO(rc, rc, -1);
}
int openat_with_path_length(int dirfd, const char* path, size_t path_length, int options, mode_t mode)
{
if (path_length > INT32_MAX) {
errno = EINVAL;
return -1;
}
Syscall::SC_openat_params params { dirfd, path, (int)path_length, options, mode };
int rc = syscall(SC_openat, &params);
__RETURN_WITH_ERRNO(rc, rc, -1);
}
int open(const char* path, int options, ...)
{
va_list ap;
@ -198,6 +209,15 @@ int open(const char* path, int options, ...)
return open_with_path_length(path, strlen(path), options, mode);
}
int openat(int dirfd, const char* path, int options, ...)
{
va_list ap;
va_start(ap, options);
auto mode = (mode_t)va_arg(ap, unsigned);
va_end(ap);
return openat_with_path_length(dirfd, path, strlen(path), options, mode);
}
ssize_t read(int fd, void* buf, size_t count)
{
int rc = syscall(SC_read, fd, buf, count);