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net/local: simplify file descriptor passing using shared filep references

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This commit removes unnecessary file duplication and memory allocation when
passing file descriptors through Unix domain sockets, leveraging the new
filep reference counting framework.

Background:
With the new filep framework, file structures (filep) can be safely shared
across processes using reference counting. When passing file descriptors
through SCM_RIGHTS control messages on local sockets, the previous
implementation unnecessarily duplicated the entire file structure.

Changes:

1. In local_sendctl() (sender side):
   - Removed allocation of filep2 structure (kmm_zalloc)
   - Removed file_dup2() call that copied the file structure
   - Now directly stores the original filep with its reference count
   - Eliminates memory allocation overhead and potential failure points

2. In local_recvctl() (receiver side):
   - Changed from file_close() + kmm_free() to file_put()
   - file_put() properly decrements reference count and handles cleanup
   - Consistent with the new filep reference counting model

3. In local_freectl() (cleanup on error):
   - Changed from file_close() + kmm_free() to file_put()
   - Ensures proper reference count management during error paths

Technical Details:
The new filep framework ensures that:
- Multiple file descriptors across different processes can reference the
  same underlying filep structure safely
- Reference counting (via file_get/file_put) manages lifetime correctly
- The underlying file object is only released when all references are gone

This change is safe because file_dup() in the receiver already calls
file_get() internally to increment the reference count for the new fd,
so the filep remains valid after the sender calls file_put().

Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>
This commit is contained in:
dongjiuzhu1
2025-11-06 15:56:59 +08:00
committed by Xiang Xiao
parent 1b6733c056
commit d1bc2800e3
2 changed files with 3 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/local/local_recvmsg.c
+1 -2
View File
@@ -177,8 +177,7 @@ static void local_recvctl(FAR struct local_conn_s *conn,
{
fds[i] = file_dup(peer->lc_cfps[i], 0,
flags & MSG_CMSG_CLOEXEC ? O_CLOEXEC : 0);
file_close(peer->lc_cfps[i]);
kmm_free(peer->lc_cfps[i]);
file_put(peer->lc_cfps[i]);
peer->lc_cfps[i] = NULL;
peer->lc_cfpcount--;
if (fds[i] < 0)
net/local/local_sendmsg.c
+2 -20
View File
@@ -65,8 +65,7 @@ static void local_freectl(FAR struct local_conn_s *conn, int count)
while (count-- > 0)
{
file_close(peer->lc_cfps[--peer->lc_cfpcount]);
kmm_free(peer->lc_cfps[peer->lc_cfpcount]);
file_put(peer->lc_cfps[--peer->lc_cfpcount]);
peer->lc_cfps[peer->lc_cfpcount] = NULL;
}
}
@@ -75,7 +74,6 @@ static int local_sendctl(FAR struct local_conn_s *conn,
FAR struct msghdr *msg)
{
FAR struct local_conn_s *peer;
FAR struct file *filep2;
FAR struct file *filep;
FAR struct cmsghdr *cmsg;
int count = 0;
@@ -117,23 +115,7 @@ static int local_sendctl(FAR struct local_conn_s *conn,
goto fail;
}
filep2 = kmm_zalloc(sizeof(*filep2));
if (!filep2)
{
file_put(filep);
ret = -ENOMEM;
goto fail;
}
ret = file_dup2(filep, filep2);
file_put(filep);
if (ret < 0)
{
kmm_free(filep2);
goto fail;
}
peer->lc_cfps[peer->lc_cfpcount++] = filep2;
peer->lc_cfps[peer->lc_cfpcount++] = filep;
}
}