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#include <init/fs/misc.h>
#include <init/stdlib.h>
#include <shared/flags.h>
#include <shared/mem.h>
#include <shared/syscalls.h>
bool fork2_n_mount(const char *path) {
handle_t h = _syscall_fs_fork2();
if (h) _syscall_mount(h, path, strlen(path));
return h;
}
static void fs_respond_delegate(struct fs_wait_response *res, handle_t delegate) {
/* The idea behind this function is that many fs implementations (e.g. for
* overlay fs) will want to forward received requests to the original fs
* implementation.
*
* Having some special support for this in the kernel makes sense - it would
* avoid a lot of unnecessary copies. However, it wouldn't be necessary for
* a working kernel - and since I want the "base" of this system to be a small
* as possible, I want to have an alternative implementation of this in the
* userland which works in exactly the same way. The libc would then choose
* the best available implementation.
*
* (note: this wouldn't be an issue if i treated everything like functions
* in the ruby prototype)
*
* This function was supposed to avoid unnecessary copies on delegated reads.
* It is being executed /after/ the write read, though. I don't currently see
* a good way to fix that. Here are a few loose ideas:
* - a fs_wait flag which requires a separate syscall to get the write copy
* - a way to "mark" returned handles
* - no write copy mark
* - mark with delegate handle
* every vfs op would go directly to that delegate handle
* probably the fastest way
* - treat open() just like in the ruby prototype
* Instead of just returning a handle, the driver would return a list
* of functions. Here's how it would work, in pseudocode:
* ```
* # for full delegation
* respond_new_handle({
* read: {DELEGATE, handle}, // extract the read function from `handle`
* write: {DELEGATE, handle},
* close: {DELEGATE, handle}
* });
* ```
*/
static char buf[1024];
int buf_size = 1024;
int size;
int ret;
switch (res->op) {
case VFSOP_READ:
// TODO instead of truncating the size, allocate a bigger buffer
size = res->capacity < buf_size ? res->capacity : buf_size;
ret = _syscall_read(delegate, buf, size, res->offset);
_syscall_fs_respond(buf, ret);
break;
// TODO writing (see above)
default:
/* unsupported / unexpected */
_syscall_fs_respond(NULL, -1);
break;
}
}
void fs_passthru(const char *prefix) {
struct fs_wait_response res;
int buf_size = 64;
char buf[ 64];
int ret, prefix_len;
if (prefix) prefix_len = strlen(prefix);
while (!_syscall_fs_wait(buf, buf_size, &res)) {
switch (res.op) {
case VFSOP_OPEN:
if (prefix) {
/* special case: rewriting the path */
if (prefix_len + res.len <= buf_size) {
// TODO memmove
char tmp[64];
memcpy(tmp, buf, res.len);
memcpy(buf, prefix, prefix_len);
memcpy(buf + prefix_len, tmp, res.len);
ret = _syscall_open(buf, res.len + prefix_len);
} else ret = -1;
} else {
ret = _syscall_open(buf, res.len);
}
_syscall_fs_respond(NULL, ret);
break;
default:
fs_respond_delegate(&res, res.id);
break;
}
}
_syscall_exit(0);
}
void fs_dir_inject(const char *path) {
struct fs_dir_handle {
int delegate;
const char *inject;
};
const int path_len = strlen(path);
struct fs_wait_response res;
struct fs_dir_handle handles[16]; // TODO hardcoded FD_MAX - use malloc instead
int handle_next = 0;
int buf_size = 64;
char buf[ 64];
int ret;
while (!_syscall_fs_wait(buf, buf_size, &res)) {
switch (res.op) {
case VFSOP_OPEN:
if (handle_next > 15) _syscall_fs_respond(NULL, -2); // we ran out of handles, which is entirely our fault.
ret = _syscall_open(buf, res.len); /* errors handled in inject handler */
handles[handle_next].delegate = ret;
handles[handle_next].inject = NULL;
if (buf[res.len - 1] == '/' &&
res.len < path_len && !memcmp(path, buf, res.len)) {
handles[handle_next].inject = path + res.len;
} else {
/* not injecting, don't allow opening nonexistent stuff */
if (ret < 0) _syscall_fs_respond(NULL, ret);
}
_syscall_fs_respond(NULL, handle_next++);
break;
case VFSOP_READ:
if (handles[res.id].inject) {
// TODO check offset
struct fs_dir_handle h = handles[res.id];
int out_len = 0;
while (h.inject[out_len] != '/') out_len++; // TODO ensure trailing slash
memcpy(buf, h.inject, out_len);
buf[out_len++] = '\0';
if (h.delegate >= 0) {
int to_read = res.capacity < buf_size ? res.capacity : buf_size;
to_read -= out_len;
ret = _syscall_read(h.delegate, buf + out_len, to_read, 0);
if (ret > 0) out_len += ret;
// TODO deduplicate entries
}
_syscall_fs_respond(buf, out_len);
break;
}
/* fallthrough */
default: {
struct fs_dir_handle h = handles[res.id];
if (h.delegate < 0)
_syscall_fs_respond(NULL, -1);
else
fs_respond_delegate(&res, h.delegate);
break;
}
}
}
_syscall_exit(0);
}
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