When a Qt application using it QSerialPortexperiences an unclean shutdown (for example, due to reception and lack of processing SIGINT), how does the serial port file descriptor affect it?
After launching an application that opens QSerialPorton /dev/ttyS0and then exits using Ctl-C, I found that it cat < /dev/ttyS0returns instantly (without printing anything), and does not wait for data (as is usually the case).
I would expect that if this is due to the fact that the open file has been processed, that it hangs around, it will be displayed in the output lsof, but lsof | grep ttyS0returns nothing. (I'm not sure how else to look for handles in a specific file descriptor.)
I understand that this is a bit of an XY problem, since I could completely avoid the problem by rewriting the application to handle it correctly SIGINT, but I would like to get a deeper understanding of what is happening here and if there is a way to restore the serial port when it is in this condition.
EDIT: As requested, here is the output strace cat /dev/ttyS0:
execve("/bin/cat", ["cat", "/dev/ttyS0"], [/* 17 vars */]) = 0
brk(0) = 0x91ce000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb76fb000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=72063, ...}) = 0
mmap2(NULL, 72063, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb76e9000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/i386-linux-gnu/i686/cmov/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\240o\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1446056, ...}) = 0
mmap2(NULL, 1460600, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7584000
mmap2(0xb76e3000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x15e) = 0xb76e3000
mmap2(0xb76e6000, 10616, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb76e6000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7583000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb75838d0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xb76e3000, 8192, PROT_READ) = 0
mprotect(0x8054000, 4096, PROT_READ) = 0
mprotect(0xb771a000, 4096, PROT_READ) = 0
munmap(0xb76e9000, 72063) = 0
brk(0) = 0x91ce000
brk(0x91ef000) = 0x91ef000
open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=1534672, ...}) = 0
mmap2(NULL, 1534672, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb740c000
close(3) = 0
fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 3), ...}) = 0
open("/dev/ttyS0", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFCHR|S_ISVTX|0660, st_rdev=makedev(4, 64), ...}) = 0
fadvise64_64(3, 0, 0, POSIX_FADV_SEQUENTIAL) = 0
read(3, "", 32768) = 0
close(3) = 0
close(1) = 0
close(2) = 0
exit_group(0) = ?
And here is the conclusion stty -a -F /dev/ttyS0:
speed 57600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R;
werase = ^W; lnext = ^V; flush = ^O; min = 0; time = 0;
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