From 78cb60b644538a33e0479f25393d6c861e3605f8 Mon Sep 17 00:00:00 2001
From: dzwdz
Date: Sun, 4 Jun 2023 20:43:51 +0200
Subject: kernel: rework /proc/ and process IDs

I'm yet to write proper docs but the TL;DR is:

Mounting /proc/ creates a new pid namespace. You're still visible in the old
namespace with your old pid, but your children won't be. You see your own pid
as 1. Current pids of children will be preserved, pids will be allocated starting
from the highest one of your children.
---
 src/kernel/vfs/procfs.c | 95 ++++++++++++++++++++++++++++---------------------
 1 file changed, 54 insertions(+), 41 deletions(-)

(limited to 'src/kernel/vfs')

diff --git a/src/kernel/vfs/procfs.c b/src/kernel/vfs/procfs.c
index 4f2bbd1..7669b78 100644
--- a/src/kernel/vfs/procfs.c
+++ b/src/kernel/vfs/procfs.c
@@ -7,6 +7,7 @@
 #include <shared/mem.h>
 
 enum phandle_type {
+	PhRoot,
 	PhDir,
 	PhIntr,
 	PhMem,
@@ -24,48 +25,52 @@ static void procfs_cleanup(VfsBackend *be);
 static int isdigit(int c);
 
 static struct phandle *
-openpath(const char *path, size_t len, Proc *p)
+openpath(const char *path, size_t len, Proc *root)
 {
 	struct phandle *h;
 	enum phandle_type type;
+	uint32_t gid = 0;
 	if (len == 0) return NULL;
 	path++, len--;
 
-	while (len && isdigit(*path)) {
-		/* parse numerical segment / "directory" name */
-		uint32_t cid = 0;
+	if (len == 0) {
+		type = PhRoot;
+	} else if (isdigit(*path)) {
+		Proc *p;
+		uint32_t lid = 0;
 		for (; 0 < len && *path != '/'; path++, len--) {
-			char c = *path;
-			if (!isdigit(c)) {
+			if (!isdigit(*path)) {
 				return NULL;
 			}
-			cid = cid * 10 + *path - '0';
+			lid = lid * 10 + *path - '0';
+		}
+		if (len == 0) {
+			return NULL;
 		}
-		if (len == 0) return NULL;
 		assert(*path == '/');
 		path++, len--;
 
-		p = p->child;
-		if (!p) return NULL;
-		while (p->cid != cid) {
-			p = p->sibling;
-			if (!p) return NULL;
+		if (len == 0) {
+			type = PhDir;
+		} else if (len == 4 && memcmp(path, "intr", 4) == 0) {
+			type = PhIntr;
+		} else if (len == 3 && memcmp(path, "mem", 3) == 0) {
+			type = PhMem;
+		} else {
+			return NULL;
 		}
-	}
 
-	/* parse the per-process part */
-	if (len == 0) {
-		type = PhDir;
-	} else if (len == 4 && memcmp(path, "intr", 4) == 0) {
-		type = PhIntr;
-	} else if (len == 3 && memcmp(path, "mem", 3) == 0) {
-		type = PhMem;
+		p = proc_ns_byid(root, lid);
+		if (!p) {
+			return NULL;
+		}
+		gid = p->globalid;
 	} else {
 		return NULL;
 	}
 
 	h = kmalloc(sizeof *h);
-	h->gid = p->globalid;
+	h->gid = gid;
 	h->type = type;
 	return h;
 }
@@ -87,36 +92,47 @@ procfs_accept(VfsReq *req)
 	Proc *p;
 	char buf[512];
 	assert(root);
+	assert(root->pns == root);
+
 	if (req->type == VFSOP_OPEN) {
 		assert(req->input.kern);
 		h = openpath(req->input.buf_kern, req->input.len, root);
 		vfsreq_finish_short(req, h ? (long)h : -ENOENT);
 		return;
-	}
-	assert(h);
-	p = findgid(h->gid, root);
-	if (!p) {
-		vfsreq_finish_short(req, -EGENERIC);
+	} else if (req->type == VFSOP_CLOSE) {
+		assert(h);
+		kfree(h);
+		vfsreq_finish_short(req, 0);
 		return;
+	} else {
+		assert(h);
 	}
 
-	if (req->type == VFSOP_READ && h->type == PhDir) {
+	if (h->type != PhRoot) {
+		p = findgid(h->gid, root);
+		if (!p) {
+			vfsreq_finish_short(req, -ENOENT);
+			return;
+		}
+	}
+
+	if (req->type == VFSOP_READ && (h->type == PhDir || h->type == PhRoot)) {
 		// TODO port dirbuild to kernel
 		int pos = 0;
 		if (req->offset != 0) {
 			vfsreq_finish_short(req, -ENOSYS);
 			return;
 		}
-		pos += snprintf(buf + pos, 512 - pos, "intr")+1;
-		pos += snprintf(buf + pos, 512 - pos, "mem")+1;
-		for (Proc *iter = p->child; iter; iter = iter->sibling) {
-			assert(pos < 512);
-			// processes could possibly be identified by unique identifiers instead
-			// e.g. an encrypted gid, or just a randomly generated one
-			// con: would require bringing in a crypto library
-			pos += snprintf(buf + pos, 512 - pos, "%d/", iter->cid) + 1;
-			if (512 <= pos) {
-				vfsreq_finish_short(req, -1);
+		if (h->type == PhDir) {
+			pos += snprintf(buf + pos, 512 - pos, "intr")+1;
+			pos += snprintf(buf + pos, 512 - pos, "mem")+1;
+		} else {
+			for (Proc *it = root; it; it = proc_ns_next(root, it)) {
+				assert(pos < 512);
+				pos += snprintf(buf + pos, 512 - pos, "%d/", proc_ns_id(root, it)) + 1;
+				if (512 <= pos) {
+					vfsreq_finish_short(req, -EGENERIC);
+				}
 			}
 		}
 		assert(0 <= pos && (size_t)pos <= sizeof buf);
@@ -136,9 +152,6 @@ procfs_accept(VfsReq *req)
 	} else if (req->type == VFSOP_WRITE && h->type == PhIntr) {
 		proc_intr(p);
 		vfsreq_finish_short(req, req->input.len);
-	} else if (req->type == VFSOP_CLOSE) {
-		kfree(h);
-		vfsreq_finish_short(req, 0);
 	} else {
 		vfsreq_finish_short(req, -ENOSYS);
 	}
-- 
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