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Share devfs dynamic major #72

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be19299
Use shared dynamic majors for devfs devices
lacraig2 May 26, 2026
0547f0a
Drop unused task switch hypercall constant
lacraig2 May 27, 2026
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3 changes: 1 addition & 2 deletions src/igloo_hypercall_consts.h
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,6 @@ enum igloo_hypercall_constants {
IGLOO_HYP_SYSCALL_RETURN = 0x1339,
IGLOO_HYP_SETUP_TASK_COMM = 0x133a,
IGLOO_HYP_SIGNAL_DELIVER = 0x133b,
IGLOO_HYP_OSI_TASK_SWITCH = 0x3337,

/* Uprobe operations */
IGLOO_HYP_UPROBE_ENTER = 0x6901,
Expand All @@ -51,4 +50,4 @@ enum igloo_hypercall_constants {
IGLOO_SYSCALL = 0x6408400B,
IGLOO_MODULE_BASE = 0x6408400C,
IGLOO_INIT_MODULE = 0x6408400D,
};
};
97 changes: 84 additions & 13 deletions src/portal/portal_devfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
#include <linux/module.h>
#include <linux/list.h>
#include <linux/atomic.h>
#include <linux/mutex.h>
#include <linux/version.h>
#include <linux/kallsyms.h>
#include <linux/file.h> // Required for fput()
Expand Down Expand Up @@ -85,6 +86,20 @@ static DEFINE_SPINLOCK(devfs_dir_lock);
// We need a class to trigger devtmpfs to create /dev nodes.
static struct class *portal_class = NULL;

/*
* Dynamic devices should share one devtmpfs major. Allocating a new
* dynamic major for every synthetic device makes /dev state unnecessarily
* fragmented and differs from how a single virtual driver normally behaves.
*/
#define PORTAL_DYNAMIC_DEV_MINORS 4096
static DEFINE_MUTEX(portal_dynamic_chr_lock);
static dev_t portal_dynamic_chr_devt;
static atomic_t portal_dynamic_chr_minor = ATOMIC_INIT(0);

static DEFINE_MUTEX(portal_dynamic_blk_lock);
static int portal_dynamic_blk_major;
static atomic_t portal_dynamic_blk_minor = ATOMIC_INIT(0);

/* * -------------------------------------------------------------------------
* Helpers
* -------------------------------------------------------------------------
Expand Down Expand Up @@ -434,6 +449,59 @@ static void ensure_portal_class(void)
}
}

static int alloc_portal_dynamic_chrdev(dev_t *devt)
{
int ret;
int minor;

mutex_lock(&portal_dynamic_chr_lock);
if (!portal_dynamic_chr_devt) {
ret = alloc_chrdev_region(&portal_dynamic_chr_devt, 0,
PORTAL_DYNAMIC_DEV_MINORS, "portal");
if (ret < 0) {
mutex_unlock(&portal_dynamic_chr_lock);
return ret;
}
}

minor = atomic_inc_return(&portal_dynamic_chr_minor) - 1;
if (minor >= PORTAL_DYNAMIC_DEV_MINORS) {
mutex_unlock(&portal_dynamic_chr_lock);
return -ENOSPC;
}

*devt = MKDEV(MAJOR(portal_dynamic_chr_devt), minor);
mutex_unlock(&portal_dynamic_chr_lock);
return 0;
}

static int alloc_portal_dynamic_blkdev(int *major, int *minor)
{
int ret;
int next_minor;

mutex_lock(&portal_dynamic_blk_lock);
if (!portal_dynamic_blk_major) {
ret = register_blkdev(0, "portal");
if (ret < 0) {
mutex_unlock(&portal_dynamic_blk_lock);
return ret;
}
portal_dynamic_blk_major = ret;
}

next_minor = atomic_inc_return(&portal_dynamic_blk_minor) - 1;
if (next_minor >= PORTAL_DYNAMIC_DEV_MINORS) {
mutex_unlock(&portal_dynamic_blk_lock);
return -ENOSPC;
}

*major = portal_dynamic_blk_major;
*minor = next_minor;
mutex_unlock(&portal_dynamic_blk_lock);
return 0;
}

/* * -------------------------------------------------------------------------
* Directory Logic (New)
* -------------------------------------------------------------------------
Expand Down Expand Up @@ -561,13 +629,14 @@ void handle_op_devfs_create_device(portal_region *mem_region)
* ===================================================================== */
if (pe->is_block) {
int major = req->major;
int minor = req->minor;
bool fixed_blkdev_major = major >= 0;

// 1. Register Major
if (major >= 0) {
if (fixed_blkdev_major) {
ret = register_blkdev(major, final_device_name);
} else {
ret = register_blkdev(0, final_device_name);
major = ret;
ret = alloc_portal_dynamic_blkdev(&major, &minor);
}
if (ret < 0) goto fail_alloc;

Expand Down Expand Up @@ -595,28 +664,28 @@ void handle_op_devfs_create_device(portal_region *mem_region)
pe->gd = blk_mq_alloc_disk(&pe->tag_set, &lim, pe);
}
if (IS_ERR(pe->gd)) {
unregister_blkdev(major, final_device_name);
if (fixed_blkdev_major) unregister_blkdev(major, final_device_name);
goto fail_alloc;
}
pe->gd->minors = 1;
#elif LINUX_VERSION_CODE >= KERNEL_VERSION(5, 14, 0)
pe->gd = blk_mq_alloc_disk(&pe->tag_set, pe);
if (IS_ERR(pe->gd)) {
unregister_blkdev(major, final_device_name);
if (fixed_blkdev_major) unregister_blkdev(major, final_device_name);
goto fail_alloc;
}
pe->gd->minors = 1;
#else
pe->gd = alloc_disk(1);
if (!pe->gd) {
unregister_blkdev(major, final_device_name);
if (fixed_blkdev_major) unregister_blkdev(major, final_device_name);
goto fail_alloc;
}
pe->gd->queue = blk_mq_init_queue(&pe->tag_set);
#endif

pe->gd->major = major;
pe->gd->first_minor = req->minor;
pe->gd->first_minor = minor;
pe->gd->fops = &pe->bdops;
pe->gd->private_data = pe;
snprintf(pe->gd->disk_name, 32, "%s", req->name);
Expand All @@ -632,24 +701,26 @@ void handle_op_devfs_create_device(portal_region *mem_region)
ret = add_disk(pe->gd);
if (ret) {
put_disk(pe->gd);
unregister_blkdev(major, final_device_name);
if (fixed_blkdev_major) unregister_blkdev(major, final_device_name);
goto fail_alloc;
}
#else
add_disk(pe->gd);
#endif

devt = MKDEV(major, req->minor);
devt = MKDEV(major, minor);

} else {
bool enable_default_mmap = (req->size > 0 || req->support_mmap);

if (req->major >= 0) {
bool fixed_chrdev_region = req->major >= 0;

if (fixed_chrdev_region) {
devt = MKDEV(req->major, req->minor);
if (req->replace) unregister_chrdev_region(devt, 1);
ret = register_chrdev_region(devt, 1, final_device_name);
} else {
ret = alloc_chrdev_region(&devt, 0, 1, final_device_name);
ret = alloc_portal_dynamic_chrdev(&devt);
}

if (ret < 0) goto fail_alloc;
Expand All @@ -661,7 +732,7 @@ void handle_op_devfs_create_device(portal_region *mem_region)
pe->cdev.owner = THIS_MODULE;

if (cdev_add(&pe->cdev, devt, 1)) {
unregister_chrdev_region(devt, 1);
if (fixed_chrdev_region) unregister_chrdev_region(devt, 1);
goto fail_alloc;
}

Expand All @@ -678,7 +749,7 @@ void handle_op_devfs_create_device(portal_region *mem_region)
list_del(&pe->list);
spin_unlock(&devfs_entry_lock);
cdev_del(&pe->cdev);
unregister_chrdev_region(devt, 1);
if (fixed_chrdev_region) unregister_chrdev_region(devt, 1);
goto fail_alloc;
}
}
Expand Down
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